in reply to @ 2016-27 14:13 UTCIt makes no difference if you alter the sprite. The only question is if any part of the game art counts as "derivative" because of the mix. I think if you make a sprite sheet or whatever, that's clearly derivative and that file must be share alike. If you make objects designed for the sprite to hold or interact with, etc, those may be derivative as well. Even code that controls special features of that sprite maybe. Other assets are less likely to be affected.
IANAL. TINLA.