Rip away! We got so many comments and compliments on them, I think there's really a need for Disney to fill, and the more of these hats they see, the more they might consider making official ones.
Plus, as you said, guys are WAY more apt to wear a ballcap than the silly top hat they sell - it's too small for many guys and it doesn't keep the sun off.
For the groom ears, just buy a cheap-o set of classic black mouse ears and cut them off, leaving a bit of the material at the base of them. We made slits in the sides of the hat and pushed the fabric left at the base of the ears through, then covered it on the inside of the cap with black felt that was affixed using Barge, an industrial-strength adhesive they use to put soles on shoes.
The bride ears were trickier and more spendy, cuz you have to buy that headband. DH removed the ears, trim and veil, and then affixed the ears to the ball cap the same way he did the groom ears. It's harder because of the sequins. Then he used Barge to affix the veil and trim at the top.
Hope this helps!