It's very easy to give spells on different levels.
Just open a file "domains.2da" and add a spell ID in level_x column in front of domain that u want.
For example, here are the healing spells with 1 level less than it should: https://ibb.co/80GV3hb
And the potions CL is not "hardcoded" too, open "spells.2da" and change "Innate"
About harm undead - it was not OP, now I'm 100% sure.
My FS was: full set, full legendaries, runes, grandstand+angel fullbuffed and 25 meters healing with 1050 dmg to undead.
SS now: have no set items, even no DM items, didn't use legendaries, only 1 runeword(not tp) and 0 summons.
SS done Abyss(the area with the highest undead concentration) 3-4 times faster than FS!
About emp healing - yes, it's not working, sorry.
And harming radius on practice is less than SoV (20ft, 6 meters)