Effecient way to offset the player's health gains?

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I'm working on a complete rebuild of my own rebalance mod, and something I wanted to do was stop the player from gaining more health after level 30 as a sort of middleground between Sawyer Mod and its Forks that reduce the level cap to 30.

I'd like to avoid using gamemode scripts for this purpose, but trying to implement this via a hidden perk just causes the player to have their health drained constantly, as if poisoned, instead of reducing their maximum health. (Even though the effect works in the opposite direction of increasing maximum Health.) No matter the flags on the effect I can't get a "Reduce Maximum Health" effect working properly.

Modding the GMST that increases the player's health per level via script has the unwanted effect of removing *ALL* health gained from leveling up retroactively, not just the health gained from post-30 levels.

Typing this out, I think what could work is actually to edit that gmst to give no health, and then have the hidden perk add a stacking +5 health bonus until Level 30, but is there a smarter way to handle this?

EDIT: Above idea didn't work. Despite this working, in theory, exactly as the Life Giver Perk, it seems adding conditions to the effect causes it to not work properly.