not sure about the bay, but i did it once at holts. my skin is between two colors and i chose the darker color first, but then i changed my mine. I went back and exchanged the brand new one for a lighter color. when they typed in my phone#, they had my purchase on file. so you can try try
I think they would let you exchange for something else, if 你有ALLERGY loh...
Especially if you exchange for something more expensive or add more items (same brand), they won't "gee-gut" you geh...