I don't know the layout of your house but, you should have a shut off valve on your water heater. shutting this off should stop the flow of hot water through your problem valves and allow work to be done.
did these fixtures leak water before? If not, debris may have gotten stuck in the valve and is allowing constant flow from the water heater. is this bathroom located adjacent to the heater? Kitchen or laundry affected?
wouldn't any solution be just as easy?
Shutting off the ball valve, cutting the copper, unscrewing fitting from the valve, screwing in new copper mip adapter and pipe?
Shutting off city line/meter, cutting copper, sweating on new ball valve, sweating on new 3/4" tubing?
of the valves...
Sure.
What state and code are you governed by? Every state has differant codes and amendments to that code. Plus additional laws on who can touch the plumbing period.
sounds like you need a longer tail piece. all tubing and sockets should bottom out without stress on the system.
I used duct tape on gas pipe the other day, seemed to keep the dirt out.
this argument is crazy since most faucets have smaller inlets or outlets(volume controlled). it does not matter that pex is "restrictive". system should be designed appropriatly.