DownUnder, SportPilot,

I don't know about the cooling period between short runs. Maybe it is a carryover from times gone by. As far as I know, annealing does stabilize the size of a hypereutectic piston. Maybe it is to a much lesser extent than with a meehanite piston, but I still do it.

But breaking-in a tapered bore engine very rich and four cycling, as you would with a hardened steel sleeve and a ringed piston, can and will potentially harm an ABC, AAC, or ABN engine.
I don't think you would argue with that.

Breaking-in is NOT supposed to remove the taper in the bore.
It isn't meant to "taper" the piston to fit either.
If this upper stroke "squeak" is completely lost, the engine may be easy to start when cold, but its power will no longer be up to par. All my MVVS ABC engines still have slight interference when cold, despite quite a bit of running time on all of them.