I've never used these, but perhaps they're what you seek:
Votan's Adaptive (Video-)Settings?
"This add-on adjusts the view- and particle distance to the current graphic load and context (normal, combat, UI hidden) to stabilize the framerate. If the view distance drops and drops, additional effects get disabled:
Distorsion, god rays and antialiasing. In this order."
Shissu's Game/AvA Booster (Last update 2017 Morrowind)
"Shissu's PvP/game booster disabled to improve various effects in the UserSetting.txt, the performance in the game went ahead in PvP.
If you find yourself in combat, the different effects are disabled depending on the selection of the level of effect for the fight 1-2. As soon as you get back from the fight out, the effects are switched on again.
In addition, you can permanently remove all effects on Eunsch."