There should be no need to edit the TGA file. Everything that BUG needs is included in the FF Gamefonts.tga files, and the only other changes are that Toads are now a toad instead of Kermit the Frog, and Pearls look like a Pearl instead of a purple clam. Plus you have a few extra mana types which won't interfere with base FfH, except that our Ice icon is different, and possibly not in the same place as 034, but you can just edit the icon reference to fix that without having to touch the graphics.
Also, I cannot remember if you stated that you have PLE icons up and running, but make sure that you cast Lichdom, and test a couple of Baby Spider battles until you have one upgrade to a Giant Spider. We were getting some Python errors which really bogged down the game in those cases. That combined with the much over-simplified unit help led to ditching the PLE (which sucked because it was pretty nice for the icon sorting/stacking deal)