Whatever floats your boat is fine of course 
.
Still, one thing does not exclude the other.
However, you don't really need a second bridge to take a port offbridge (and it would make the "offbridge" become "onanontherbridge" 
) compare also with this:
What I would do, as hinted before, is to apply a "static" default configuration that will be restored whenever only mechanical (press the reset button) actions are performed.
This configuration would have (permanently) the offbridge port (on vlan10 as you made it) and have a "diff configuration script" stored on the device itself.
This script should be capable - if manually run - be capable of restoring the original default configuration. I.e. no need to "upload" a new configuration (that will soon be lost, or confused with that of another device, etc.), the operator connected to the offbridge port would only need to invoke the script on the device.