Which actor?
Most respawning actors are part of leveled lists - there the actor doesn't respawn, but the list creates a new actor. Enabling / disabling the actor does nothing to the leveled list, it will work like it did before. Disabling the leveled list however stops the creation of new actors.
The few rare handplaced respawning actors (like the adorning fan) will likely (haven't tested, merely guessing) stay disabled
if they're hand placed and a persistent reference.