Just slap some grunge on it to create a derivative work. CCP has the ultimate call over what’s owned and displayed in their IP.
I’d only reserve custom portrait backgrounds for Star Citizen type whales willing to pay out the ass for pixels. However, what would likely be more healthy for the game is connecting portraits (even more custom requests from the art team) to player progression goals/unlocks (i.e. lose a couple rorqs, get a special portrait background to publicly showcase your indifference #alreadyreplaced)
