Most of the time if you’re carrying a muzzle loading rifle, you are carrying it in one hand up near the rear sight balance point - or cradled in your left arm if you’re right handed. If you’re super bothered by it, it sounds like you would need a gun with a fowler type guard on it. Retrofitting one To the Kibler Colonial would be difficult, since the existing inlets for the rifle guard are wider than most any Fowler trigger guards you could find.
It would require setting the triggers in deeper and filing away most of the remnant of the existing trigger guard inlet. All of which may still not be possible given available wood clearance for new guard inlet after removing enough of the existing guard inlet.