Adding the flag is pretty simple, just DL a .dds file converter, go to
C:\Program Files\EA Games\Battlefield 2\mods\bf2objects_client\staticobjects/common/textures then find "flags_c" convert it to a JPEG or something with your dds converter, then open the new JPEG with a pic editor like pain or photoshop, and then paste your new flag over the American one or which ever your editing. After that, convert the file back to a DDS and put it the mod that you want. Be sure that the DDS for your mod has the same directory as the file you copied, but instead of it being in BF2, it's in your mod.
you got it, I just recently figured it out myself.