>>1849522most solvents should not damage the original paint job, only paint strippers would attack it. Depending on the adhesion between the acrylic and the old topcoat, a light oil solvent such as Shellite (camping stove fuel) or possibly even kerosene, if given some time to soak in, could assist in debonding. It wont dissolve any paint but it may slowly seep into the poor bond between the original paint job and the acrylic spray paint, encouraging more flaking of the top layers. The best way to do this is to wrap the tube in tissue/cloth/paper damped with the solvent, then wrap some cling film or baking paper around that to reduce the evaporation (so you dont waste as much liquid), and then let it sit for like... between 10 minutes and an hour, then see if the acrylic paint flakes off easily.
I would avoid paint thinners, alcohol, etc. unless you run out of other options. It will be messy since you will dissolve and smear the acrylic paint which means a lot of solvent used, a lot of tissues used, etc. Save that kindof stuff for the final cleanup getting in the nooks and crannies, try to remove the majority of the paint by flaking it off mechanically, with some chemical assistance in the debonding.
its possible that lots of rubbing of thinners or spirits would smear and minutely dissolve some of the original paint. Its unlikely this would go far enough to make any real difference to the protection the paint offers, but might be visible in the light as a more matte area. Test any solvent first on an inconspicuous area before going ahead with something.
