I would like to have a simple script apply a permanent night-eye ability to all vampire NPCs in the game, so that it is next to impossible to sneak around them. Rather than give this spell manually to all the vampire NPCs, I want a script to check and see if an NPC is a vampire, and if so, then give them the spell. This way it is also applicable to any mod-added vampire NPCs as well as the vanilla ones. I don't want to just change the "Hunter's Sight" spell that all vampires have to be permanent, because then that would also effect the player if they become a vampire.

Any ideas? Thank you in advance if anyone is able to help with this.

Sneak detection is based more on the potential detectors own Sneak skill level than spell effects active. Just bump up the Sneak level on the base vampire. Players have to earn that.