diff --git a/src/api/SIGCM2.Api/Controllers/UsuariosController.cs b/src/api/SIGCM2.Api/Controllers/UsuariosController.cs
index d86e562..15d27fd 100644
--- a/src/api/SIGCM2.Api/Controllers/UsuariosController.cs
+++ b/src/api/SIGCM2.Api/Controllers/UsuariosController.cs
@@ -246,6 +246,30 @@ public sealed class UsuariosController : ControllerBase
         return Ok(MapToPermisosResponse(result));
     }
 
+    /// <summary>
+    /// Replaces the grant/deny override sets for a usuario.
+    /// Requires administracion:usuarios:gestionar.
+    /// </summary>
+    [HttpPut("{id:int}/permisos/overrides")]
+    [RequirePermission("administracion:usuarios:gestionar")]
+    [ProducesResponseType(typeof(UsuarioPermisosResponse), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status400BadRequest)]
+    [ProducesResponseType(StatusCodes.Status401Unauthorized)]
+    [ProducesResponseType(StatusCodes.Status403Forbidden)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    public async Task<IActionResult> UpdatePermisosOverrides(
+        [FromRoute] int id,
+        [FromBody] UpdatePermisosOverridesRequest request)
+    {
+        var command = new UpdateUsuarioPermisosOverridesCommand(
+            Id: id,
+            Grant: request.Grant ?? [],
+            Deny: request.Deny ?? []);
+
+        var result = await _dispatcher.Send<UpdateUsuarioPermisosOverridesCommand, UsuarioPermisosDto>(command);
+        return Ok(MapToPermisosResponse(result));
+    }
+
     private static UsuarioPermisosResponse MapToPermisosResponse(UsuarioPermisosDto dto)
         => new(
             RolPermisos: dto.RolPermisos,
@@ -266,6 +290,11 @@ public sealed record PermisosOverridesShape(
     IReadOnlyList<string> Grant,
     IReadOnlyList<string> Deny);
 
+/// <summary>UDT-009: PUT permisos/overrides request body.</summary>
+public sealed record UpdatePermisosOverridesRequest(
+    IReadOnlyList<string>? Grant,
+    IReadOnlyList<string>? Deny);
+
 /// <summary>Create user request body — nullable to catch missing field scenarios.</summary>
 public sealed record CreateUsuarioRequest(
     string? Username,
diff --git a/src/api/SIGCM2.Api/Filters/ExceptionFilter.cs b/src/api/SIGCM2.Api/Filters/ExceptionFilter.cs
index f583aed..f566bf3 100644
--- a/src/api/SIGCM2.Api/Filters/ExceptionFilter.cs
+++ b/src/api/SIGCM2.Api/Filters/ExceptionFilter.cs
@@ -169,6 +169,35 @@ public sealed class ExceptionFilter : IExceptionFilter
                 context.ExceptionHandled = true;
                 break;
 
+            // UDT-009: permiso override validation errors
+            case InvalidPermisoCodesException ipce:
+                context.Result = new ObjectResult(new Microsoft.AspNetCore.Mvc.ProblemDetails
+                {
+                    Type = "about:blank",
+                    Title = "invalid-permiso-codes",
+                    Status = 400,
+                    Extensions = { ["invalidCodes"] = ipce.InvalidCodes }
+                })
+                {
+                    StatusCode = StatusCodes.Status400BadRequest
+                };
+                context.ExceptionHandled = true;
+                break;
+
+            case GrantDenyOverlapException gdoe:
+                context.Result = new ObjectResult(new Microsoft.AspNetCore.Mvc.ProblemDetails
+                {
+                    Type = "about:blank",
+                    Title = "grant-deny-overlap",
+                    Status = 400,
+                    Extensions = { ["overlap"] = gdoe.Overlap }
+                })
+                {
+                    StatusCode = StatusCodes.Status400BadRequest
+                };
+                context.ExceptionHandled = true;
+                break;
+
             case ValidationException validationEx:
                 var errors = validationEx.Errors
                     .GroupBy(e => e.PropertyName)
diff --git a/src/api/SIGCM2.Application/DependencyInjection.cs b/src/api/SIGCM2.Application/DependencyInjection.cs
index 6c5db6a..d71d9c2 100644
--- a/src/api/SIGCM2.Application/DependencyInjection.cs
+++ b/src/api/SIGCM2.Application/DependencyInjection.cs
@@ -60,6 +60,7 @@ public static class DependencyInjection
 
         // Usuarios/Permisos (UDT-009)
         services.AddScoped<ICommandHandler<GetUsuarioPermisosQuery, UsuarioPermisosDto>, GetUsuarioPermisosQueryHandler>();
+        services.AddScoped<ICommandHandler<UpdateUsuarioPermisosOverridesCommand, UsuarioPermisosDto>, UpdateUsuarioPermisosOverridesCommandHandler>();
 
         // FluentValidation validators (scans entire Application assembly)
         services.AddValidatorsFromAssemblyContaining<LoginCommandValidator>();
diff --git a/src/api/SIGCM2.Application/Usuarios/Permisos/UpdateUsuarioPermisosOverridesCommand.cs b/src/api/SIGCM2.Application/Usuarios/Permisos/UpdateUsuarioPermisosOverridesCommand.cs
new file mode 100644
index 0000000..bd4953f
--- /dev/null
+++ b/src/api/SIGCM2.Application/Usuarios/Permisos/UpdateUsuarioPermisosOverridesCommand.cs
@@ -0,0 +1,7 @@
+namespace SIGCM2.Application.Usuarios.Permisos;
+
+/// <summary>UDT-009: Command to replace the grant/deny override sets for a usuario.</summary>
+public sealed record UpdateUsuarioPermisosOverridesCommand(
+    int Id,
+    IReadOnlyList<string> Grant,
+    IReadOnlyList<string> Deny);
diff --git a/src/api/SIGCM2.Application/Usuarios/Permisos/UpdateUsuarioPermisosOverridesCommandHandler.cs b/src/api/SIGCM2.Application/Usuarios/Permisos/UpdateUsuarioPermisosOverridesCommandHandler.cs
new file mode 100644
index 0000000..29a90e3
--- /dev/null
+++ b/src/api/SIGCM2.Application/Usuarios/Permisos/UpdateUsuarioPermisosOverridesCommandHandler.cs
@@ -0,0 +1,81 @@
+using SIGCM2.Application.Abstractions;
+using SIGCM2.Application.Abstractions.Persistence;
+using SIGCM2.Application.Common;
+using SIGCM2.Domain.Exceptions;
+
+namespace SIGCM2.Application.Usuarios.Permisos;
+
+/// <summary>
+/// UDT-009: Handles PUT /api/v1/users/{id}/permisos/overrides.
+/// Validates overlap and catalog existence, persists new overrides, returns updated effective set.
+/// </summary>
+public sealed class UpdateUsuarioPermisosOverridesCommandHandler
+    : ICommandHandler<UpdateUsuarioPermisosOverridesCommand, UsuarioPermisosDto>
+{
+    private readonly IUsuarioRepository _usuarioRepo;
+    private readonly IRolPermisoRepository _rolPermisoRepo;
+    private readonly IPermisoRepository _permisoRepo;
+
+    public UpdateUsuarioPermisosOverridesCommandHandler(
+        IUsuarioRepository usuarioRepo,
+        IRolPermisoRepository rolPermisoRepo,
+        IPermisoRepository permisoRepo)
+    {
+        _usuarioRepo = usuarioRepo;
+        _rolPermisoRepo = rolPermisoRepo;
+        _permisoRepo = permisoRepo;
+    }
+
+    public async Task<UsuarioPermisosDto> Handle(UpdateUsuarioPermisosOverridesCommand command)
+    {
+        var grant = command.Grant ?? [];
+        var deny  = command.Deny  ?? [];
+
+        // 1. Overlap check — grant ∩ deny → 400
+        var overlap = grant.Intersect(deny, StringComparer.Ordinal).ToArray();
+        if (overlap.Length > 0)
+            throw new GrantDenyOverlapException(overlap);
+
+        // 2. Catalog existence check
+        var allCodes = grant.Concat(deny).Distinct(StringComparer.Ordinal).ToArray();
+        if (allCodes.Length > 0)
+        {
+            var existentes = await _permisoRepo.GetByCodigosAsync(allCodes);
+            var existSet = existentes.Select(p => p.Codigo).ToHashSet(StringComparer.Ordinal);
+            var faltantes = allCodes.Where(c => !existSet.Contains(c)).ToArray();
+            if (faltantes.Length > 0)
+                throw new InvalidPermisoCodesException(faltantes);
+        }
+
+        // 3. Load usuario
+        var usuario = await _usuarioRepo.GetByIdAsync(command.Id)
+            ?? throw new UsuarioNotFoundException(command.Id);
+
+        // 4. Persist — use WithPermisosJson to get updated FechaModificacion
+        var newOverrides = new PermisosOverride(grant, deny);
+        var updated = usuario.WithPermisosJson(newOverrides.ToJson());
+        await _usuarioRepo.UpdatePermisosJsonAsync(
+            updated.Id,
+            updated.PermisosJson,
+            updated.FechaModificacion!.Value);
+
+        // 5. Return updated effective set
+        var rolPermisoEntities = await _rolPermisoRepo.GetByRolCodigoAsync(updated.Rol);
+        var rolPermisos = rolPermisoEntities
+            .Select(p => p.Codigo)
+            .OrderBy(c => c, StringComparer.Ordinal)
+            .ToArray();
+
+        var effective = PermisoResolver.Resolve(rolPermisos, newOverrides)
+            .OrderBy(c => c, StringComparer.Ordinal)
+            .ToArray();
+
+        return new UsuarioPermisosDto(
+            UsuarioId: updated.Id,
+            Rol: updated.Rol,
+            RolPermisos: rolPermisos,
+            Grant: grant,
+            Deny: deny,
+            Effective: effective);
+    }
+}
diff --git a/src/api/SIGCM2.Domain/Exceptions/GrantDenyOverlapException.cs b/src/api/SIGCM2.Domain/Exceptions/GrantDenyOverlapException.cs
new file mode 100644
index 0000000..5e2ac12
--- /dev/null
+++ b/src/api/SIGCM2.Domain/Exceptions/GrantDenyOverlapException.cs
@@ -0,0 +1,16 @@
+namespace SIGCM2.Domain.Exceptions;
+
+/// <summary>
+/// UDT-009: Thrown when the same code appears in both grant and deny arrays.
+/// Maps to 400 { title: "grant-deny-overlap", overlap: [...] }.
+/// </summary>
+public sealed class GrantDenyOverlapException : Exception
+{
+    public IReadOnlyList<string> Overlap { get; }
+
+    public GrantDenyOverlapException(IReadOnlyList<string> overlap)
+        : base($"Los siguientes códigos aparecen en grant y deny simultáneamente: {string.Join(", ", overlap)}")
+    {
+        Overlap = overlap;
+    }
+}
diff --git a/src/api/SIGCM2.Domain/Exceptions/InvalidPermisoCodesException.cs b/src/api/SIGCM2.Domain/Exceptions/InvalidPermisoCodesException.cs
new file mode 100644
index 0000000..048569d
--- /dev/null
+++ b/src/api/SIGCM2.Domain/Exceptions/InvalidPermisoCodesException.cs
@@ -0,0 +1,16 @@
+namespace SIGCM2.Domain.Exceptions;
+
+/// <summary>
+/// UDT-009: Thrown when grant or deny arrays contain codes not in the Permiso catalog.
+/// Maps to 400 { title: "invalid-permiso-codes", invalidCodes: [...] }.
+/// </summary>
+public sealed class InvalidPermisoCodesException : Exception
+{
+    public IReadOnlyList<string> InvalidCodes { get; }
+
+    public InvalidPermisoCodesException(IReadOnlyList<string> codes)
+        : base($"Códigos de permiso inexistentes en el catálogo: {string.Join(", ", codes)}")
+    {
+        InvalidCodes = codes;
+    }
+}