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.
[matt re sonnets] I think a story context is useful for the Sonnet game, full stop. The problem with the Hiawatha thing was that no-one knew who on earth these people were, or what to do with them. That's why I added the Noah's Ark theme as the unifier for the new one. [rab] Reunifying could be quite fun. I'd quite like to see what Survivalist Barbie would do to Joe Orton, or how a Mandalayan fishmonger might take on a henpecked dragon or two :)