Paul, These finishes can be thought of more like a set epoxy than a solvent release finish of any kind - once their catalyzed an different material is created so you can't dissolve it like a "thinner" does. Theoretically most solvent release finishes can be reused indefinitely and I once read of a wood worker back in the 1930s that crushed up the old shellac 78 RPM records and dissolved them in alkyhaul to make his own wood working finish during the Great Depression. Best I know you have to abrade this cat finishes off - too bad the manufactureres don't use a thin sealing coat of shellac under them so that once you get an armor piercing shell through the finish you could at least remove it w/o potential wood damage.
There is no thinner for catalyzed finishes. Any chemical that affects the finish will destroy it rather than dissolve. Some catalyzed finishes can be attacked with one or more of the more aggressive chemical paint removers, some are loosened or softened a bit with heat, and others resist pretty much anything except mechanical removal, i.e. scraping or sanding.
A pox on these finishes, we mainly deal with electric guitars which are mainly finished with these UV and other catalyzed poly. The thicker finishes can be attacked with heat but mechanical scraping and sanding is still required if bare wood is needed for a new finish. The cat finishes also tend to penetrate and bind to the substrate (wood) in a very aggressive manner making removal of all traces of old finish difficult without a significant sanding cut back near impossible. New finishes have some difficulty keying to the remains of this impervious finish.
Short story, if you can key up the previous finish, try to refinish over it. This is not a great solution as the new finish will have a tendency to chip off the old layer but the alternative of complete strip, especially on a thin wood like acoustics, is an expensive and time consuming fix.
Note, while I know this will draw the crabs from the shellac advocates, don't use a cat finish over a shellac finish - you can use nitro over cat or shellac but not cat over nitro or shellac. In my experience the cat finish will lift and crack over time if put over a less resilient flexible sealer. PRS, Fender and many others adopt this position also - they use a poly sealer/base coat followed by a nitro finish schedule on various models.
Hello David, sorry mate, didn't make the association due to the international nature of such communications and my lazy and indolent attitude to anything not having strings. A good chemist knows such things, eh! Things are fine, the business is sound and thriving and I am training my apprentice to take over at the end of the year as I embark on bringing my guitar manufacturing project on line. A fork in the road and most enjoyable one at that. Gis a call anytime David - still at Hadow Place. R.