Maybe there is a way to modify it I don't know. Also, I'm guessing you don't want to, but you could buy a male shirt in a similar color (like from a craft store) cut out the picture and attach it to the new one... (hehe sorry I'm guessing you wouldn't want that). Looking online I'll I see is changing a man's shirt to a women's shirt but not vice versa.. : (
Hahaha. Same thing happened to me, but with a Keep Calm and Do't Blink shirt. My friend's mom got it for me for a buck at goodwill, and wouldn't take my money. So I just wear it around like "Yeayuh, I got it goin'! *jiggly jiggly jiggly*" Sooo yeah. I would suggest selling it to a friend and using money to buy a mens shirt. Or... Y'know... Give it to me...
if this is still relevant, if they won't take returns, you can give them as gift to some girl you really care about (sister, cousin, friend, girlfriend etc) (preferably if she's brony/pegasis)
This gave me a chuckle. Can't say I've ever bought a shirt intended for the opposite sex, but I'm sure they'll let you exchange it with the men's version (if there is one) if you explain the situation. If not, you could always just give it to a girl or hang it on your wall like Rockout suggested. Only problem I've ever had with my own pony shirts is that they're all light cotton, and I'm definitely a heavy cotton kind of guy. Something about light cotton shirts that makes them feel somewhat form-fitting...which would be fine if I were buff, but I'm not quite there just yet.
