If your kegs or bottles ahve yeast in them, you likely lysed a lot of yeast and can get some pretty nasty flavors, burned-rubber style. If there wasn't any yeast in the kegs, you should be fine, although I hadn't thought of overcarbonation. I would thaw them out 100% (at which point they'll be pretty much uncarbonated, I think) and then hook them back up to serving pressure for a set-and-forget slow carb.
I can't be arsed to keep up this list of what's in the fermenters, but hey, check out the cool brewery I'm opening up!
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