Re: Is rigth or wrong way to do truss rod adjustment on a vintage style instrument?
No problem at all doing it this way. It's quick and clean and gets the job done with little risk to anything. Far better than detuning and retuning the instrument!
That said, I usually find it unnecessary. You should be using narrow #1 or smaller screwdrivers to adjust vintage style truss rods, even though the truss nuts would seem to call for a #3 screwdriver based on the way they look. Using a #1 off center is the way to do it. Then the most you need to do is pull a pickguard (if that, even). FWIW, some of Fender's own original "vintage" instruction manuals state exactly this: use a screwdriver with a head no wider than 1/8".