A) "Essential" means just that - change an Essential Variable, make [& test] a new PQR.
B) Solar "B" flux works fairly well for the first two or three quadrants. Then the weld heat makes the stuff flake off as the welder puts a root in the last quadrant, and then it is "sugar city". Cut out one of the fluxed welds and put it on the kid's desk.
C) What does work is s/s Tig wire with an integral flux; some are flux coated, some flux-core. My welders call it 'mud rod' because the normally 'wet', fluid weld puddle behaves like a glop of mud when using the fluxed rod to run the root. And this too is an Essential Variable.
Now comes the 'fun part' -- how do you address out-of-Code welding? If you are not willing to quit/be fired, you will always be a 'tame' inspector on a short, harsh leash. Me, I'd tell the owner that I can't sign for the out-of-Code work, than ask him if he would like to sign the papers or should his brilliant sone sign the papers. You may loose the job, but you'll sleep better if you refuse to sign for junk work.