Color re-map in art programs?

[Marscaleb]

Hello, I'm wondering what sort of options there are for performing a color re-map of a sprite or a texture. I personally use GIMP, and I would hope there is a reasonable way to do it in GIMP, but I guess I'll take whatever I can get.

The best method I have come across so far is the color re-mapping tool in Slade. It works exactly the way I would expect it; I can select a range of colors I want to change and then a range of colors to change them to.
But it is a bit of a hassle to use in art development. If I need to tweak the art, I have to export it and then re-import it. If I want to change the palette or use a different palette, it is a lengthy hassle to bring in this new palette.

Is there any wya to do this in GIMP, perhaps a plug-in that someone has made? If not, is there another program that makes it easy to re-map the colors without jumping through the hoops I have to if I want to do it with Slade?