Depends on how well the surfaces bonded and how much was used. A spare amount might result in joins that could yield to a little finessing. A lot of glue probably means the plastic is now one solid piece and cutting is your only option.
I have had some success using mineral spirits to "loosen" the bond. Used sparingly along the join and then gently prying to get the parts apart. I've only ever used this technique with recently glued parts using Testors liquid (purple label), you know, the "oh cr@p!" moment when I realized that I glued it wrong.
Paul