I will need to look into how GIMP handles the color palette for GIFs, fundamentally BIFs are similar, but I know the indexing of the palette matters (0 = transparent, 1 = semi-transparent(?), any other restrictions?) for the MTW engine. You can run GIMP in Indexed mode, with private indexed palettes, and you can import palettes, so I think it's doable it would just be a question of maintaining the order throughout the import/edit/export process. If worst comes to worst, a temp palette file can be saved when importing.

The BIF color palette is only 16 bits (5/6/5 or 6/6/4 RGB iirc), not sure how each primary is translated to/from 8 bit (clipped or normalized). RSW's source for the BIF reader is available, I'll look through that to see how it's done and how the compression works. GIFs also can have multiple frames, I believe they are treated as separate layers in GIMP so that should be easy (and GIMP lets you preview GIF animation, might be useful with unit animations).

Info on BUF files is hard to find. Any ideas on how these work?