working with valve stem retaining ring?

Forum newbie, DIY plumbing novice here, so forgive me if I struggle with terminology...

Replacing tile behind faucet in old house (1920s) with separate hot n cold valves for bathtub. There are retaining rings on valve stems which loosely hold escutcheons in place. I can see nut where stem meets pipe but it's difficult to access even after I demo'd the old tile. Can't seem to remove the escutcheons or the rings which maybe are part of stem. I can slide escutcheons closer to wall but there's not much play and can't just slide them off due to rings. Are those rings threaded on? No flat surface for wrench but would one twist them off with channel locks or vise grips? A little reluctant to put too much stress on 'em.

Should I just try my best to remove valve stem and get new fittings? Any advice appreciated, including general info about this type of stem/fitting.

https://www.flickr.com/gp/shutterbuggery/388nN3

While you have the wall removed, cut out old faucet and replace with new pressure balanced faucet.

Just grab hold of the part on the end of the threaded nipple with some pliers and take it off. That threaded nipple is only holding the escutcheon on.