He messed it up, for sure. But not permanently. It's fixable.
FWIW, there are very few competent gunsmiths in the black powder revolver theater. Keep us posted. I've done this repair myself a few times. Normally, the way an idiot would "open up clearances" is to mill the face of the cylinder, If this is what he did it's a super simple fix; replace the cylinder with a new one. Since all Pietta parts have been CAM/CAD since 2002, this would require nothing other than a gunsmithing screwdriver set and a mallet to drive out the wedge. If it's a pre-'02 gun, you may have to do some fitting. Do you know the date code of the gun? (either Roman numerals or two capital letters in a box on the frame) That will help a lot.
Now, if he did 'something else' to open the gap (you never know with these hacks!) we may have to explore this in depth. But we'll cross that bridge when we come to it.