1) Maybe using the mapping functions of Hijack, but I don't know for sure if this specific function can be created.

2) Not that I've played with the Wendy filters (yet), but IIRC, once the current running list has been built, the player has no knowledge of where the tracks came from (they're now just a list of individual fids). Therefore it can't go back and recheck whatever playlist you selected and look for songs no longer filtered out when you remove the filter...

/Michael