I think that you've identified a real sore spot with just about every QLA type of muzzle design. When barrels are rifled all of the way to the muzzle, the crown usually is slightly beveled or tapered.
The problem is thataltering it in an uneven fashion will adversely affect the point of impact.
One option is to get rid of the false muzzle and crown it properly.
The other would be to risk fixing it where it's located.
I doubt that a coning tool would work satisfactorily to produce such a small taper on the edge of the rifling.
On the other hand,aproperly sized round ball or round fixture loaded with a fine abrasive lapping compound and rotated by hand might produce the desired results if workedpatientlyover a period of time.
What's the worst that could happen? You'd need to cut off the false muzzle and recrown it. But by fixing it you would have an improvedrifle that was bettersuited to your personaltaste.
It's like the old saying, "Don't let fear interfere with obtainingyour dreams."
If you want it fixed then eitherdo it when you're good andready or just live with it as it is.
The choice is yours.