Yeah backing out the two screws closest to the headstock and the other two closest to the butt end a tad more... is a tried and true, well-known approach for adjusting truss rods on these axes that were sadly at that time not engineered for easier rod access. It works, is done every day, we do it too, and can be perfectly safe.
It is unnerving though if you have not done it prior or had the opportunity to see it done. I felt the same way the fist time I saw it done and then did it. This is when I was not cursing Leo.... for the poor rod access as well as lack of break angles on the G strings.... OTOH the manufacturability of Fenders was at that time and possibly still second to none and that was Leo's primary goal, to take the costs out of manufacturing and exploit the use of less expensive standard cuts of lumber. I think he nailed that one.
Can you imagine if Jimi and Eric did not have Strats? It's likely that some of the greatest tunes of the times might be shorter if someone had to schlep a Les Paul all the way through Purple Haze or Layla....
