Well, I'd definitely choose the chap in Rolex St. James over doing it myself.
I see nothing wrong in asking about doing 'a simple task' like this. I would never have known about the blade thickness of the screwdriver or what type of loctite to use without asking.
Just get a good set of screwdrivers and never pay for resizing a bracelet again. I am always surprised how people are afraid to open and close a screw. Buying a bottle of loctite is a good idea though. But don't get the super strong one.