I made two different key lime recipes, one is really moist and tart, the other not so much but I don't want to waste the second set of cupcakes. Is there anything I can do to make them more "tart lime" tasting before I ice them? 

AMake a simple syrup of lime juice and sugar and water, and brush the tops. Or just use lime juice brushed on, but I would refrigerate afterward.

AMaybe you could look up a key lime cake recipe that uses a simple syrup and brush it on, or fill them with lime curd. I think there is a paula deen recipe on food networks website where she does this. This happened to me a few months back. When I iced them, I made the buttercream with mostly lime juice as the liquid and added a little cream and zest. Then I filled them with lime curd mixed with sweet cream( cream cheese, whipped cream and sugar).

AMake sure you're using actual Key lime and not "regular" lime.

Make a syrup with Key lime juice and sugar and brush it on the layers/cupcakes.

AOk great. Thanks for the feedback. I think I'll try both (curd and simple syrup) and see which I like better. Thanks!

The curd sounds great!!!

AI'd love a good key lime cupcake recipe, too.