I had a CU change on my most recent assessment, never mentioned the seal fairy visiting, they didnt care. All they want to see is your paperwork, you arent as daft as a lamp post and your test results pretty match align with whats on your test results schedule.
I also showed a CU change and partial rewire for my first DI assessment, I didn't notify building control prior to starting, worse case i would have used the firm i was working for to sign off.
In the event you didn't pass the assessment, and it seems very rare. then they would likely charge you for a second site visit. you could then notify building control and pay 10% on top which i think is standard. as out of time notification. like most people these days they want your money like the niceic!! prosecutions by building control for such things are as rare as unicorns!
once assessment is passed you can notify it yourself on the niceic portal. you are meant to notify within is it 28 or 30 days of the job. but that runs from date on the test results apparently. so date your test results a couple days before the assessment visit.
its a bit like chicken and egg, you cant notify as not in a scheme, but cant join scheme as youve no notifiable jobs, they know this and just play along so you can notify afterwards.
As for pulling fuses, its frowned upon, but its your own risk, if it goes badly wrong , you will likely not know much about it! only you can make the risk assessment on pulling one. but dont make a habit of it!