Originally posted by kobayashi
Theoretically correct but you need some special software (paint shop pro) to do this. Also I strongly urge you not to mess with your default Civ2 files.
Begin a scenario and mess with it there. Many people use a units.bmp instead of units.gif to get around the problem, you can edit units.bmp using the MS paint program from windows. You can just take a template from any of the scenarios you download - I use units.bmp exclusively myself.