You get to decide which job you show the assessor. I would think the vast majority of electricians on this site adhere to the regulations on all jobs, but there are some jobs you do where you just know you ticked all the boxes and there's no grey areas, so pick that job. Remember it at the time and make a note so you don't forget that that is the job you want to show the assessor. Perhaps a bit over the top, but it means I don't have to think back over all the jobs before assessment time.
Yes, you just let the customer know, or rather you ask their permission. You can let them know at the time that this may be a job that gets assessed, or at a later date. No customer has said 'no' so far.