The conspiracy aliens never came back because brophy visited their home world first and wiped them out with a fly swatter and a can of raid.
His perfect form cannot be assumed by changelings. See John Ales's failure to do just that. Was John Ales a changeling? Neither can Bran Brophy be assimilated, so there may have been difficulty including him in the script. Perhaps he will save Tuvok.
Brophy assimilated what was left of the Borg Collective after 2378. The XBs in Season 1 of PIC were the ones he deemed too boring and uncool to be a part of his new galactic order!
I've always wondered if Brian Brophy was any relation to Kevin Brophy who was the star of the short lived series Lucan back in the seventies? JB
Brian Brophy was supposed to make a cameo for the final scene, but his asking price was too high so they got someone cheaper instead.