How can I alter a save game so that I can change say a custom-made spell's casting cost and success chance?

I kind of finished Morrowind like 5 times, including the expansions. Now I want to heavily mod it, but no matter how heavily modded it gets, I just can't seem to get the right feel for my customization, so I want to start with editing custom spell values and such through the save file.

Can someone help?

http://mw.modhistory.com/download-95-1662 or http://mw.modhistory.com/download-95-5289 can edit ess files.
You basically have to know what you're looking for, or you're going to be confused. Things are not clear to see like the Construction Set.
And one wrong edit and you can wreck your save file, so make a back-up of it first.

It would probably be simpler and faster if you just made a little mod that created the spell you want. Then add that spell to yourself in-game. (then delete the old from your spell menu)

I have enchanted editor, and I know where to look, but when i want to edit the spell's values, it gives me some crazy numbers such as the hex values and sumsh*t. The only thing that is clear is the Spell Cast cost. So how to edit spell success chance, magnitude of spell, area affect, and duration?

See, that's what I mean by confusing.
I've been using EE for a long time, but a lot of the stuff I have no idea how to successfully edit. And there is no guide or documents for EE.