You don't really replace them in the slab, most of the time you find other avenues to place them.
I've seen them run below the ceilings, boxed out.
And I've seen them in attics.
If the repipe is in the attic, special attention should be placed on the insulation.
In cold climates, I don't like any insulation between the warm areas of the home and the pipe.
I lay a blanket of insulation over the pipes to trap the warmth coming up through the ceiling.
I don't believe in pipe wrap for prevention.
I've repaired many a pipe that had "pipe" insulation.
PEX can be a good product for repiping.