bbPress.org

Do not use the move-it plugin until it is radically updated.

There is no proper way to split/merge topics because it would affect many plugins which track things based on the topic id.

Since bbPress never had action hooks for split/merge, all plugins in existance are ignorant of such changes happening and you risk corrupting your forums.

Split/Merge is on the agenda for bbPress 1.5, so maybe a year from now it might be possible. But again, all plugins that store tracking information on topic id’s will need updating, including a dozen of my own.

So yes, you could manually do it, or even force it via move-it, but you will break your forum sooner or later.