There is currently a small problem in Skyrim where a permanent ability will not be affected by perks that change spells magnitude after the player acquired the ability.

For example, a spell that damages the player's stamina by 4 per second. If I add a perk AFTER the player acquired the ability with Mod Spell magnitude x2, the value won't change to 8 stamina per second.

This is usually not a big deal but I need to have an ability on the player and I want to be able to change it's magnitude.

Right now, the only way to do it is to reset the ability on the player via a script, but since I have a lot of abilities like this, refreshing every single one with a OnUpdate script might be too much...

Is there any workaround ?

Not tried it yet, but given I have a similar issue, I was thinking of flipping a global on the Condition--in theory, if a condition becomes false, and then true again, the Ability would automatically be reset to the new appropriate value; then all you'd have to do is toggle the global before you apply the Perk, and then flip it back afterwards. But, like I say I've not got around to trying it out yet, so it might not work :/