The interior doors have a metal door frame, molded to look like it has
the trim pieces. Its appears to cover the wallboard on both sides. It
seems pretty firmy attached, though the fasterners are not apparent,
The carpet wraps around the bottom and extends to the middle.

That's not really much of a description, but it's just a molded metal
door frame; the house is from the 60's

Has anyone any experience in taking these out and installing a
pre-hung door?

Without screwing up the carpet?