I am doing a cake for an engagement party and I am planning on icing it in BC, but I'd like to do stripes and possibly some other accents in fondant. I'm going to do most of the decorating tonight, but can I put the fondant on today or will it get 'mushy' by the party tomorrow?

no I have iced decorated cakes in buttercream and accents in fondant and added them to it the night before and nothing happens.

Go ahead. The fondant won't be mushy by tomorrow.

Me too....should be fine.

I've done it before - fondant holds up just fine on BC - even longer than overnight! We were eating cake 2 days later (BC with fondant) and it was still great!

Been there, done that! No worries. Just go ahead and do what you have to do