Unless you give them control of the skins themselves, but I understand what you mean.
Another idea would be to add an early build P-51D without the tail fillet and a birdcage P-51B, effectively doubling the skin slots for the P-51s. What I like about this is that the skins would be more historically accurate and could be featured on the exact type of model used in real life. The P-51 is one of those late model US planes with lots of colorful schemes - another 64 skin slots would help alleviate much of the pressure; might even be enough. Though I think they would still fill up. But at least its an idea that works within the constraints of the existing framework.
