Sched 8 is reasonably new to me but I am well aware of similar listings and procedures from other countries. I have included a couple of links to interpretations of the lists. Neither are great explanations and each leaves some room for personal interpretation.
https://www.casa.gov.au/sites/g/file...-operators.pdf
AOPA Pilots' Guide to Preventive Maintenance
The AOPA guide has a pilot feel to it and I think could be improved upon in certain areas.
You can soon see by comparing the two that they have similarities and each may help answer questions raised by the other.
I doubt the owner can go far wrong even if the interpretation is off beam.
Provided the work is done satisfactorily and certified then he has made an honest go of it. We have seen from this thread, and a similar one running concurrently, that we have different interpretations probably based on our backgrounds and experiences...... and desires.
Neither of those documents really address the protocols to which the work is normally carried out. The supply and fitting of spares is barely touched upon and yet Part 21 is one of the bigger sections in the regs. Many owners would feel that identifying a P/N and sending an email to Aircraft Spruce is SOP.
I doubt many are interested in researching the actual procedure as it makes little difference to the end result in their eyes.
I am talking side windows again here but it can quickly become much more complicated than either of the linked document indicates.
I think in reading them we should appreciate they are both very much 'dumbed down' versions of the actual rules and protocols.
The LAME, or A&P, works with this stuff on a daily basis and should have a fair idea of the operating requirements of the rules and how best to navigate about them. I am pretty confident he won't be 100% correct but at least if you work within his version then that is one less person that could potentially be upset.
All I expect from the owners would be good communication and records. I would talk them through the log entries, over the phone even if necessary.