Can you decorate with it? or Can it be covered with buttercream?
That's ok! I probably wouldn't cover it w/fondant. I think it would soften your fondant to mush. You could use it as a filling and use a layer of bc over the cake then cover with fondant. You'd have to refrigerate the cake but I have refrigerated fondant many times with success. Just don't touch it once you take it out until the condensation has evaporated on the cake!
Good luck with it! 
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One more question...Can I put chocolate decorations on it? I'm making the decorations out of chocolate.
I used to teach cake decorating classes and whenever I taught the fondant class, we always told the students NOT to use whipped cream or whipped icing for the layer of icing under the fondant. There is way too much moisture in this kind of icing and it compromises the fondant.
You can definitely put chocolate decorations on the whipped icing without having difficulties except for maybe if the chocolate pieces are too heavy and you are putting them on the side of the cake (not on the board). The chocolate pieces may slip.
Good luck and can't wait to see the cake picture posted.
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