This is a curiosity question, as I have not yet found a definative answer. I plan on testing this, but thought maybe a quick answer may save me some time:
* Is it possible to add member switches that are running a differnet version of Junos?
Obviously, proper procedure would be to install same verison on new switch before adding, but what happens if this isnt done? Does the master upgrade/downgrade Junos on the newly added switch?
You can also have the VC upgrade the newly added switch by adding the 'set virtual-chassis auto-sw-update' configuration knob beforehand. This way a new switch is upgraded to the same version as the rest of the existing VC.
Sounds like, as suspected, best practice is to match versions prior to adding a member.
Thanks for the clarification on this.