Many people seem to have had a problem with trying to change the name of a speaker, and finding that the name reverts to it's original. Most solutions offered suggest adjusting settings in Apple Home or HoimeKit. But I had this problem even though I don't use Apple Home. Sonos support werent able to help, but I think I've found a solution.
You need to use a mac connected to your iphone or ipad. In finder, navigate to Library/Application Support/Sonos/jffs/cached_hh. You'll find a file named Sonos– followed by a long alphanumeric. Open this file in text edit and use Cmd-F to search for the original name of the speaker. Change the name to the one you want to use. Close the file.
That should fix it. It worked for me.
Good luck,
Colin White