I just cut the wrapper cap off a bottle of red wine from the Cotes du Rhone and the top of the cork is partially covered in mold. Should I open the wine or save myself the trouble and take it back to the store?

This is a common occurrence and not an indication of any problem with the wine in the bottle. Just wipe off the mold with a damp paper towel, pull the cork, and wipe away any mold that may remain around the lip of the bottle.

Of course, if the wine itself is bad, then take it back, cork and all.