Is there any way to remove powder coat without marring the substrate? How would the part have likely been prepared for coating? This is on a master cylinder. Do you think it could be returned to an original appearance?

Regular old paint stripper works fine

I've had good luck with Tal-Strip aerosol paint remover.Usually find it a Checker/Cragens/Shuckers.

Hot tank.

As long as the part was clean it would have needed nothing else prior to powder coating. The powder isn't that thick so if you don't see casting lines or the rough as-cast finish then it's likely been touched up before it was coated.