Adding penalties to items

[capacitatedflux]

In theory, I've figured out how to add a negative stat modifier by looking at the positive stat modifiers (like the Intelligence increase on Lab Coats). Actually implementing it is making me wary, though, because I really, really don't want to break anything.

 

I've gotten to the part where I copy the original modifier "EnchClothingAgility" to a new .esp in order to rename the EditorID/Name and effect to a negative value. Of course it includes the FormID of the original, so I'll have to change that/add a new one... which brings me to my first question. How do I pick a new FormID that'll fit without overlapping anything? Or am I able to just pick one that isn't currently used in my specific .esp and the load order will sort it all out?

 

Secondly, will negative values even work? It's letting me change the Magnitude value under "effects" in the copy/pasted version (which I assume would overwrite the original EnchClothingAgility globally, based on the shared FormID) to a negative number, but, again, don't want to test and risk borking the whole thing.

 

Short version: I want to patch the AnS Backpack mod to add a penalty for simply wearing the larger backpacks (without regard to the actual carry weight). I know I'll have to add in the effect to each backpack entry, but getting the effect in the first place is where my issue currently lies.

 

EDIT: And of course, right after I push submit I found the answer to the first question in a completely different tutorial. Second question remains, though.