Dont quote me on this, but I think your problem is going to stem from the fact that the lens in your helmet isnt rated (most likely) high enough to withstand the impact of a paintball. It may actually be strong enough, but if its not an actual paintball mask, theres really no way for the referee to KNOW that its capable of protecting your eyes, so they wouldnt let you use it. That would be like going to play in a pair of sunglasses that you may know will stop a paintball, but since the referee doesnt know that, he has to assume they arent safe enough....It also doesnt help that your helmet wouldnt look like a conventional paintball mask, and that would make any park owner leery of letting you use it at their place.
I'd say your best bet would be to take a paintball mask and modify it to look similar to a Fett helmet. That way youve got the original eye protection from the paintball mask, which is the most important part. I dont think the field officials will really care one way or the other about how much visibility your mask provides you. Its the eye/face protective aspect that they must look for.
I dont have a paintball mask in front of me, but I cant imagine a conversion would be all that difficult. The goggle part of the mask would be a good place to build a Fett helmet off of. You could shape the front cheek pieces around the front part of the paintball mask, and then find something to cover the back of the mask, forming the back part of the Fett helmet. The most difficult part would probably be forming the top part (round dome) of the helmet. Your best bet would be to convert a batting helmet or some sort of polymer military helmet by hacking off certain pieces and attaching it to the rest of the setup.
It might be an interesting project, but in all honesty youre going to have a hard time getting the park officials to let you wear it, you will probably be pretty uncomfortable, and I dont know about you, but I think I'd be afraid that a paintball impact would not only hurt my face but also break my mask. You will probably have to do some extensive gluing and I just dont think glue will give enough strength to stand up to that kind of impact......best of luck to you bud!