So I dug out the Battle Realms CD the other day, adjusted my GeForce GTX 780's settings to improve the game as best I could.. but still wanted more. So I found out about that h2oTool, and had no problems editing a texture (the placement square for the Dragon Clan), though the results weren't great (it didn't crash the game, however a simple change from orange to blue caused it to look very strange) but regardless of editing or not, the shadows become black squares.
Is there any documented guide to editing the .tga files that make up the textures of the game? I'd love to be able to adjust them, even if it's minor.