I have loose faucet handles. I do not see a set screw.

I need to install a new prv in my house. I've put a gauge on a hose bib outside the garage and turned the adjusting screw clockwise but no change on the gauge. It stays at 90 psi, drops to 80 or so when running water. I am bleeding off pressure at another bib after each adjustment. So presuming I've done all I can I guess its time for a new one. The prv is threaded onto copper male adapter and has a union on the other end. Having the union is fine but I still have to spin the valve to get off the other fitting. I don't trust my sweating skills to try this the right way. So my question, finally, is can I unscrew the bonnet (cone shaped part of valve) off while taking off/putting on the new one without damaging the valve. It is too close to the wall to spin without taking it apart. This is a Watts 3/4 inch aub and is 5 1/4 inches end to end. If I can't find one with same dimension then its plan B anyway. Thanks!

Good day! Looking for some help. I honestly have tried to have plumbers come out and do this but no luck where I live. I am doing a kitchen remodel and the new sink sits 3 inches lower. The current drain disposal height is just at the drain wall level so it needs to be lowered. I figure these are my options: -Switch the stand tube and the drain? (This will lower the drain 4+ inches and have least amount of work question is if this is okay to have the vent and stuff above the drain instead of below wherever they meet up at? -Use only the current stand tube and put a splitter that one end goes to stand tube and other goes to drain? -Tear some of the wall up to find where these pipes meet the vertical tube and then add a split for a new drain or stand pipe?