According to Chris Lewis :
According to HA HA Budys Here :
I suppose in an old home, wired with knob & tube, or 2-wire NM cable, you're
not permitted to replace the 2-prong outlets with new 2-prong outlets either,
huh?

Specific exemption. It's pretty hard to find a two prong receptacle here
in any case.

I should add, as an additional example of where grandfathering does not work
is that of GFIs. If an outlet needs to be replaced in a location that now
requires GFI, you're required to add GFI. Ie: "shaver outlets" in bathrooms.

You could even replace it with a 2 prong. But the circuit must now be GFI
protected.

See the electrical wiring FAQ.

Ditto.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.