Do pex fittings need to be replaced when installing a new water heater?
PEX pipe won't slide off the fittings if spun because they are on there through compression and not screwed on. I've spun the crimp style fittings without issues but never spun the style you have before but from what I've read, you can spin them with out issue. If you decide to cut the pipe, remember you'll need a spreading tool to reconnect the pipes or use something like SharkBite fittings. You can reuse the brass fittings by cutting the ring with a knife and then heating up the plastic pipe and then bend it back and forth until it comes off. From what I've read, you can do the same with the plastic fittings but be very careful not to cut or overheat them. I'd just replace the plastic ones instead.