As much as I admire your thorough work, when I price to change a CU, I price to change a CU, not carry out a PIR and full correction of remedial works. Any faults found that require fixing are charged as an extra, not included in my price. I dont carry out any more than a Ze / Zs check and an inspection of the main earth bonding prior to carrying out the job. In my opinion you are making more work for yourselfs. I make it very clear in my tenders what is and is not included, if faults are found that cause the new CU to trip then it is extra money to fault find them. It rarely takesme more than 30 mins to an hour though to sort out issues like that. As long as I dont leave anything in a condition that is less safe than it was before I carried out the job, it can wait to be fixed when the client agrees to pay for it.