I've done it both ways. When I used SMBC to do the FBCT, I had some trouble getting the exact colors I wanted. I think that was because I used gel colors instead of candy colors. I used a crusting buttercream to get a bright red and black for Spiderman, and when I put the FBCT on SMBC there were no problems.
I don't see why not. You probably wouldn't even have to freeze it... just chill it and it gets damn hard, but freezing might be a good idea anyway. Getting the dark colors with SMBC is a pain though. Gel colors don't work as well, and candy colors leave a distinct flavor is you use them in high quantities.
I've never done a FBCT, but SMBC will set up very solid and I'd imagine it would work fine.
Thank you all very much. The colors shouldn't be a problem, as the figure in question is all shades of yellow, which I've noticed SMBC tends to, anyway. I just think SMBC tasts so addictively good...
....wow, I'm sitting here salivating over cake at not quite 6 in the morning! 
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