In rereading the OP I see we never really answered the question.


Various paint strippers do exist that might soften the paint/primer. A gel (as opposed to a liquid) version will tend to not run or spread on it's own. Applying only on the shell's ID and using the face of the shell as the "DMZ" while care is taken during the mechanical work to apply then scraping off will be the key to not effecting the outer surface of the shell. This method takes some time and reapplications. The results might still want a proper chasing or single point scraping to get down to bare metal.


Next time the frame gets painted there are methods to shield the threads. It's too bad the painter didn't use them this time. A small amount of prep can save a lot of clean up. The lack of doing so suggests the painter wasn't concerned of wasn't experienced. Perhaps a fuller pre painting discussion of expectations was in order. Andy.