Yeah I know it sounds a bit eccentric, but let me explain. My idea is to make Morrowind's racial abillities and birthsigns the same as those in Oblivion (i.e. give them the same bonuses, powers, etc.).
If you really want to, you can change the names of the spell effects in Gameplay -> Settings, under the Magic tab.
Changing the name of "Weakness to Magicka" into "Weakness of Magic" doesn't change the spell's effect. "Weakness to Magicka" makes you weak to non-elemental offensive spells, while "Weakness to Magic" makes you weak to all offensive spells, elemental or not.
I guess I could just combine "Weakness to Magicka" with the "Weakness to frost/fire/shock" effects. That would basically be the same as "Weakness to Magic". Same could be done with "Resist Magicka".
You can't necessarily add new effects, but you can often create a spell with an insignificant effect and have a global script that imitates the effect you want. For Reflect Damage you wouldn't be able to do even with that ( unless you knew the target and the character using the spell ), but with the script extender you might be able to.
Ouch, that sounds complicated (the word "script" always makes my head hurt :tongue: ). Come to think of it, the "Reflect Damage" effect only occurs in the Tower birthsign, so an easy solution would be to leave it out ("Beggar's Nose" is better anyway)