The fitting and certifying is naturally the realm of the LAME or A&P.
That is commonsense and is indeed the ways the rules are written.
It doesn't matter how many times you see the owner maintenance fallacy repeated on the internet it still doesn't make it any more correct.
This of course is not correct.
You do not have to be an LAME or A&P. Nonsense proliferated by these people who think they are have the only God Given right to work on aircraft.
I have personally made and installed dozens of windscreens, and possibly a hundred of more side windows. Very few LAMES would even be capable of manufacturing them. I have blown bubble canopies and presently making a windscreen and sliding canopy for a Hawker Hurricane replica. It only needs skill and patience, not a massive ego.
HD