So I duplicated the AbResistFire magic effect and turned it into a Fire and Forget spell effect. It seems to work fine, except that if I cast it multiple times, it adds the effect multiple times instead of replacing the existing effect. Any ideas what might be causing this?

I have not been able to confirm whether the effects stack or not though.

AbResistFire has the Effect Archetype Value Modifier. This is the cause of the stacking.

Change this to Peak Value Modifier, then set Assoc Item 1 to Resist Fire.

Add a (custom) keyword to your effect. Close and re-open your magic effect

Then set Assoc Item 2 to your keyword.

When your effect is re-applied, it replaces rather than stacks.

http://www.creationkit.com/Magic_Effect

Ah, okay, that makes sense. Thanks!

What is the purpose of adding the custom keyword and second associated item?

Edit: Nevermind, I see. Add the keyword and check the "Dispel effects with these keywords" box to dispel re-castings of the same spell. Doesn't look like I need to (or even can) add the keyword as "associated item 2" though.

"Dispel effects with these keywords" doesn't actually seem to work all the time, but setting the Assoc. Item 2 to your keyword will ensure it doesn't stack. The reason you couldn't add it may have been because you didn't close & re-open the Magic Effect window.

Regardless of issues with "Dispel effects", you wouldn't want to check this box. If it works as intended, if you have an effect, and then re-apply the same effect, if you have this checked, it would dispel the effect.

Using a keyword in Assoc Item 2, if you apply an effect that has a keyword, ie myKeyword, then anytime you apply a magic effect it replaces (if the magnitude is higher) the existing magic effect.

This part is important in the understanding of how PeakValue Modifiers work

If you have a magic effect where the Assoc Item 1 is MagicResist, and Assoc Item 2 is myKeyword.

You also have another magic effect where the Assoc Item 1 is DamageResist and Assoc Item 2 is myKeyword.

If you apply both magic effects, neither one will overwrite each other, because at least one of the Assoc Item criteria differs.

This method allows the same Assoc Item 1 value to be modified by multiple effects, but allows for unintended stacking.

For example, if you wanted to have to two types of magic effect which increased Magic Resist to stack together, but you didn't want each effect to stack by itself.

Still using Peak Value Modifier, you would set both Assoc Item 1 to Magic Resist, but you would give each magic effect a different keyword, so the 1st magic effect may have a keyword , myKeyword, and the 2nd magic effect has a keyword myNewKeyword.

By setting Assoc Item 2 on the 1st magic effect to myKeyword, and

setting Assoc Item 2 on the 2nd magic effect to myNewKeyword

both magic effects can be active on the target, but neither magic effect will stack multiple times.

Egocarib - I believe that is correct. I don't recall cycling the magic effect window after adding the keyword.

Heilghast - Thank you for the extended explanation of the difference between associated item 2 and "Dispel Effects". I'm going to keep using the "Dispel Effects" option for now on these particular spells because I have multiple resist spells (one per element) and don't want to be able to have more than one active at a time. On future changes or additions I will have to remember to use the associated item 2 instead though.

Thanks again everybody.