You can definitely do it in photoshop, so I'm imagining GIMP can also do it, but I don't know how. In photoshop you'd do it via either Batches or Scripting. In some programs they call that sort of thing Macros. Probably GIMP calls it one of those three things, and usually you just turn on "macro mode," make your changes to one image, and then save that as a macro. Then point it at a directory, load a macro to apply, and it does those steps to all the images in question.
Hope that helps!
