I have a long rifle, not a hooked breech, that I can convert from Percussion to flint, locks have matching sideplates. Drum for the percussion and touch hole liner have matching threats. Percussion sideplate has a cutout that seats around the drum. It is a .40 cal that I used to hunt squirrel.
For those who fought for it, Life has a flavor the protected will never know.
The short answer is yes, I have converted at least half dozen TC Renegades and Investarms percussion guns to Flint, then installed a drum to accommodate a nipple to convert back to percussion. For liability reasons I am reluctante to post my procedure here ,but you will need a drill press and be familiar with drilling and tapping holes,then the original percussion lock will have to be altered to accommadate the new drum. A bench grinder and an assortment of good files are also needed tools as well as the proper size drills and taps. A good dremel tool with assorted stones will also be helpful.
Google Fort Chambers ,they are a blackpowder shop here in Franklin Co. that I believe will do this conversion.