Well, this is about the reverse flow (counter to “Update PCB from Schematic”).
Two examples of situations where this makes sense, are:
You changed one or more footprint(s) in the Layout, and you want to capture it in the Schematic so that the change is not “lost”.
You are working on a connector and you reassign the pin mappings to make the routing easier (you may have changed several pins while you are getting this job done).
Electronic CAD programs support such workflow (e.g. ECO features); it is quite a natural thing to do, even when there is only one person doing both schematics and layout.
I haven’t found a way to do that with KiCad. Is this supported?
It is possible.
In the layout, File->export->Footprint association (.cmp) file
In the schematic, File->Import association file (or Back icon, on top bar rightmost icon)
I’m afraid it is not possible yet. Same feature as reassign FPGA pins.
It is in the wishlist for v6, I don’t think it will be ready for 5.1.
For swapping pins, look up ‘swap pins action plugin’ by Mitja Nemec. That search will also show other options if you don’t like it, but it worked well for me.