Like for like requirements

Hi, I know like for like replacement is classed as maintenance and a MEIWC isn't required. With an alteration to a circuit the new work has to comply with the latest BS7671, so some of the existing installation will need to comply also to allow the new work to comply, like RCD (if required), bonding, existing equipment rating and condition etc.

Am I right in thinking that for like for like this is not required? So if there was no bonding or RCD protection you could still change a light fitting for example.

What if there was no CPC at the light and you were fitting a class 1 or class 2 fitting? Or getting crazy, no CPC on a socket front change?

Thanks.