I have a bag of Edna's crusting creamcheese frosting in the freezer, and some of Sugarshack's crusting bc in the fridge (only a week old). Is there any reason why I can't combine these two in order to use up some of my leftovers? The cake I'm making this week isn't an outdoor cake, so I don't need to worry about the cream cheese melting. I will be doing both piping decorations and covering the cake with the frosting.

Nope, no reason whatsoever!