It seems that the relevant option is:
and then you just add the checksum under that. Worked for me for the void.bmp when I tested. The only 2 other aircraft that have some customization options afaik are Fokker DXXI and I-16 (some early versions). Interestingly, in DXXI it's
NoWheelspats. You must add a cat to your custom skins, though