I downloaded an armor mod a few days ago . The armor has no enchantment so i used CK to add enchantments to the armor . I added " Fortify Alteration , Fortify Conjuration , Fortify Destruction , Fortify Illusion , Fortify Restoration (Magnitude 30 each) " , then saved the .esp (the esp of this mod was actived when loading ) file . I startesd the game , put on the armor , it works .
I played with this armor for a few days and overwritten the quicksave many times . Until one day , something bad happened : I don't want this armor mod any more . So I deleted the .esp file of this mod. Then I loaded the quicksave and played for a few days and overwritten the saves , Then I discovered that the spell cost reduction effect still existed in fact , it seems that the cost of every spell has already been overwritten , and didn't change back at all .
Somebody please help me , what should i do to change the spell cost value back to normal ? (I'm playing the latest patch 1.4.27.0.4)

To sum up - you used a mod that adds some buffs to your toon, played with it on - saved. Exited [while still wearing it] - removed the mod etc. Restarted and the buffs are still there and you want to get rid of the buffs?

You can try re implementing the mod - load your save, take the armor off and check if that removes the buffs. If so, save there, exit and delete the mod.

I have modified the armor enchantment many times before I recognize this problem . Add enchantment " Fortify Alteration , Fortify Conjuration , Fortify Destruction , Fortify Illusion , Fortify Restoration (Magnitude 75 each) , remove the mod , overwrite saves , add enchantment " Fortify Alteration , Fortify Conjuration , Fortify Destruction , Fortify Illusion , Fortify Restoration (with different magnitude i can't remember how much) again , remove the mod , overwrite saves , added " Fortify Alteration , Fortify Conjuration , Fortify Destruction , Fortify Illusion , Fortify Restoration (Magnitude 30 each) , remove the mod , overwrite saves , until I discover this problem . The original spell cost value has been overwritten many times . I hope there is one console command can reset the cost value ,or there may be a method to fix it .
I don't think you resolution will work . still thanks .

up

This has been a problem since Oblivion or even before.
When you use a mod that damages (e.g. eat/sleep mods) or buffs (e.g. your example) your Actor Values and deactivate that mod while it is still in effect,
those modifiers get stuck on the player - creating corrupt Actor Values.

Unfortunately, there is no way to remove them until someone releases an "Actor Values Fixer" mod.
I've looked at building this mod (because I have such a mod for Oblivion called Actor Details).
But unfortunately, there is no way to do it in Papyrus.
We'll need to wait until SKSE is released.

Did you try casting Dispel (if there is such a Spell) on your self?
Or did you try going to a healer?
In Oblivion, these somtimes worked. It really depended on the type of Magic Effects corrupted your Actor Value.

Why don't you just load your old save where you had the armor, take it off (stats should go back to normal) then remove the mod?

IF that doesn't work just remove the mod then player.setav skillname alteration 20 or whatever you want them at, where they would be without the armor.