It is actually quite difficult to put into words.
As a christian, we cannot spereate our beliefs from what we do. We dont have that get out clause.
So we have to make best guesses from what we know.
What we do and write and speak and everything, is judged. Putting something in the public arena that you dont agree with, and dont think God agrees with, comes back on you when you are judged, either which way.
I do think though, that christians make decisions daily, and this one probably wouldnt rank high in importance to God if we did or did not do the words on the cake.
At the end of the day, the instructions regarding this I dont think are covered in the bible[as far as I know], so we can only guess.