I don't remember seeing a "Jump Height" Variable in an Actor Form (not in my CK currently to check) ... there is no Element called "Jump" mentioned on the wiki, though; so my guess would be that this is hard-coded.
- If there IS a variable, then a MagicEffect should be able to increase it.
- If there is NOT a variable, then I doubt one will do it (and, indeed, nothing - scripts included - may do it)
Just in case, check the RACE Forms to see if that has a Jump Variable (but I don't think they do either)
And finally: While I've seen my player character jump, on occasion, I have never witnessed a jumping NPC ...