As long as you don't get caught, but if you did your own design it wouldn't be theirs, so you would be the only one who would know WTF your shirts all about.
and if I'm right you can make 7 changes to a design to make it your own.
say you did IRON MAIDEN you can't copy-rite IRON MAIDEN and sell that shirt, but IF you did
IRON MAIDEN you still wouldn't sell the shirts as its not IRON MAIDEN they only do it one way and that's their way and that's wot sells shirts....but if you had copy-rite or a band gave you permission then why not go for it.
this is in my opinion, I wouldn't get one if not an original...