These "roles" would be filed under the random set.
Neutral Killer:
Randomly picks between Arsonist and Serial Killer
Adding this option would then remove the need of "Exclude Non-Killers" from Random Neutral.
Exclude Non-Killers shouldn't exist on Basic Neutral or Adv. Neutral anyway, as its 100% serial killer or arsonist respectively. (until you add more killers anyway)
Town Detector:
Randomly picks between Sheriff, Investigator, possibly Lookout, and Detective
Town Killer: (Name might need tweaking)
Randomly picks between Vigilante, Jailor, and possibly Bodyguard.
In the case of adding Cult Roles (I hope you do eventually)
Random Cult
Randomly picks between the roles allied with cult, like cult detector, cult blocker(escort/bg?), whatever gets added.