What do you mean by "change it"? I don't want any of my designs highly altered with other than a few small details.
But you can gift/trade/resell the design so long as you dont sell it for more than the 300
you bought it for!
but also, just because your friend really likes it, dont give it away if you dont want to and like the design yourself.
its rightfully yours, and you can do what you want with it, but im just saying you shouldn't let someone make you give it to them.