I can't comment specfically about NAPIT, but my experience (ELECSA, NICEIC) is that a CU change was sufficient for many years, but now is no longer so. I always used to offer a CU change as I did lots of these and it was easy to find one local for a site visit that was unlikely to throw up any issues!
I discussed that with my NICEIC assesor last time (Jan/2023) and he commented that he now needed to see something more, but was somewhat flexible, and suggested a new circuit even just comprising just one socket adjacent to the CU change would likely be OK. Though I think I'd be reluctant to offer something so minimal just in case it wasn't.