Each game fork has its own rules. Additional forks may be possible if the particular game would allow it at the time. Reunifications must be legal in all affected forks.
Shit. I was going to do a move today, but I notice that the tea leaves of fate are disappearing down the plug-hole of destiny (getting trapped in the U-bend of eternity etc) and it's nearly time to go home. Bugger it. Got so caught up in 'Notes and Queries' at Orange I neglected this. (And I have also done some work today, woohoo!).