The mod Additional Placements allows you to place any stairs and slabs on any axis. If a block is placed in a way, that can not be covered by vanilla blockstates, it is instead replaced by a block with the id: additionalplacements:originalmod.originalblockname

It would be neat if BlockSwapper could accomodate for this and allow seamless replacements of additional placements blocks (while maintaining their boardstate) if a compatible block is used to replace it.