Usually, depending on the joint, cutting, puttying and sanding are the only ways to get things apart. However there are two other methods I've used are Freezing and Oven Cleaner mixed with Ammonia (the least desirable for lots of reasons).
1.) I've actually been able to separate parts from glued up kits, including whole fuselages of aircraft and car bodies by soaking them in water for a couple of days (to insure water penetrates any gaps), placing them into a plastic bag, and immediately popping them into the freezer. This process de-laminates joints by allowing water to penetrates the joint gaps and expanding slowly, forcing the gap open. You may still need to do some repair work later. It doesn't always work, depending on the strength of the glue and type of glue, but it has worked for me in the past. Keeping the model loosely in a plastic bag ensures all the parts stay in one location and don't "ping" off into the freezer (don't ask me how I know).
2.) By soaking the model in Oven Cleaner mixed with a half cup of Household Ammonia for 24-48 hours (most oven cleaners use Ammonia as an active ingredient), you can sometimes weaken some glues to a point where the joint will deteriorate. Unfortunately, some plastics also become brittle during the wait, and both Ammonia and Oven Cleaner are smelly and require safety precautions (like gloves and eye protection, and a face mask).
Other solutions such as using acetone or further "un-gluing" with additional liquid cement usually just result in a breakdown and "melting" of the surrounding plastic. Hope this helps.
VR, Russ