At the moment when you rebuild geometry all volumes will be rebuilt. Is it to have a ‘Quick Rebuild’ (and ‘Quick Rebuild for Current Level’) that only rebuildings volumes that have been modified since the editor has been opened / the geometry last built? For BSP this could be extended to include other BSP that changed BSP overlaps with.
And when you rebuilt geometry, all BSP loses their light maps. Is it possible to not lose them for BSP that hasn’t been modified since the last geometry rebuild as part of this ‘Quick Rebuild’?