How do I write metadata to BACKUP file?

My master videos are stored on a NAS.

When I start a new PP project I copy the video files to my PC as a "working copy"

During editing, I add file metadata to the "working copy" eg Keywords.

How can I copy/sync this metadata change from my "working copy" to my "master copy"?

I envisaged creating against the "working copy" in PP, a sidecar file for the metadata that can be copied to the "master copy" location later. Thus having the keyword data available long after the "working copy" has been deleted.

How do I achieve this, or is there a better way?

I am running the latest PP on a PC on a LAN with a NAS for storage.