I think I build more than I shoot sometimes. For certain I spend the most time building, mostly flintlocks.
Sometimes It is necessary to drill and tap the touchhole into the breech plug for the touchhole liner. Then is necessary to pull the breech plug, then take a Dremel or similar tool to smooth things down. The touchhole itself, after drilling, needs to have the inner threads smoothed out.
WHENEVER you have to remove the breech plug, be sure to put anti-seize on the threads. I have a hard time thinking about a reason to pull the plug on a finished muzzle loader, but I guess it could happen.
Pedersoli, and many other manufacturers will have the percussion drum drilled into the breechplug, making it impossible to remove the plug without first removing the percussion drum.
Personally, I try hard to install a touchhole liner at least 1/8" in front of the plug. I also like to chamfer the liner on the inside - that will prevent a cleaning patch from snagging on the liner. There are several old-fashioned tools made for reaching into the breech for the chamfering process, but I just use my Foredom flex-shaft tool with a ball on the end for that chore.