I'm not sure how refresh.metered behaves when there is a network device change, but I assume it will, yes.

And I'm pretty sure NM lets you set all network connections metered, i.e.

  nmcli connection modify $CONNECTION connection.metered yes

See https://unix.stackexchange.com/questions/364927/networkmanag...

Someone on reddit stated that snapd will update snaps regardless of what value `refresh.metered` holds when updates are postponed long enough. Unfortunately, I haven't been able to verify whether this claim is true or false.

Canonical should be up front about this type of information.