It is encouraged and appreciated if all nodes connected to the MVMA area are upgraded to current Stable.

It is possible to upgrade remote nodes that do not have internet access.

It is possible to upgrade nodes without downloading the current Stable firmware onto your computer.

I think everything can be upgraded via wired LAN, Wi-Fi LAN, DtD, or RF.
Only not via a tunnel.

Remotely...
if you insert
'nc8q-mesh-server.local.mesh/mesh/'
between
'http://' and 'downloads.arednmesh.org/'
in the 'Advanced Configuration' page settings
everything can be upgraded and/or installed.

Once the value is edited and 'Save Setting' is clicked,
just browse to the Administration page,
click the 'refresh' button and voila!