In Jellyfin, I can simply navigate to Settings > Administration > Dashboard > General > Paths and update the cache and metadata paths without need to shutdown or otherwise manually mess around with folders and permissions.
This should be a standard feature in the UI for Plex administration.
Especially helpful for having Plex containerized, with the metadata as a separate drive/mount point where if the main Plex container needed to be rebuilt, the administrator could simply re-attach/remount that drive and adjust the path to pick up the pre-existing data.
PMS runs as a non-privileged user and does not have open permission to create directories or make mounts wherever it wants
-OR-
Are you referring to changing the default PLEX_MEDIA_SERVER_APPLICATION_SUPPORT_DIR and other variables to be user definable at next restart so PMS will read them and, if valid, continue to startup ?
At present, there are no defaults. Each platform is assigned locations as part of the startup process, It would be a lot of work, if even possible (most important), to implement on all the platforms.
I will think about this and how to implement for the various NAS platforms and then discuss with the team. I know that not all platforms will be able to support it.
The biggest issue will be in moving the data while PMS is live (making a safe copy)