Saving to a gif format and choosing the color palette

[SpongeBob]

Thank you @rich2005 & @Ofnuts,

So yes I would like to edit the colormap of the output pictures.

Here a video what I was able to do under CS6

http://sendvid.com/b88mfkjs

As we can see here first I remove a blue color ( passing from 32 colors to 31 colors) then I switch one blue into orange.

So is this possible under GIMP ?