only needed for rebuilt engines

Might be a good question for the service manager at the dealer; that person will be most familiar with any TSBs that may have come out.  But otherwise, just break in per the owners manual (usually says something like don’t redline it or use cruise control the first 1000 miles; that’s typically adequate). If you want to, you can change the oil after the first 1000 miles.  Or don’t, it usually doesn’t make that much difference.

The bigger thing is to stay on top of oil changes long term, over the life of the engine....

I was "also said" that the world was flat.  The only time I have seen "break in oil" specified is from brand new crate engines (GM Performance) and rebuilts like from Powertrain, ATK and Jasper.  Follow the manufacturers (rebuilders) recommendations, not what your friends say.

This is not in owners manuals but some say that when you drive your car out of the dealership to rev your RPM to 300 for 15 minutes in order to seal the piston rings. It is also said that first 500 miles, one should change the oil and then change it again at the regular interval. Is this true?