I'm trying to find out if it's possible to mess around with the missions because I'm going nuts with the whole supernatural stuff in Thief 1. Is the editor hard or if anyone here feeling charitable and would be willing to help?

All I want is that all undead creatures can be wacked with 1 hit regardless of type and weapon I use. I thought of skipping the levels or just remove them with the editor but that seems like skipping half the game, if not more so I might as well try to play it but with some advantages to avoid the annoyance of the combat mechanics. Unlimited holy water or some similar cheat is also okay.

trust me, you are better off overcoming your fear of the dead.

It's not about fear really, I love undead creatures in most games but not in this and if there's a creature I have a huge hatred for it's zombies. The only game I enjoy them is in Plants vs Zombies due the comical effect, otherwise I can't take them serious or any interest. :(

Anyway, I managed to finish the 4th mission so at least it's over for now.

I'm not a huge fan of zombies either, but it's worth sticking it out to finish the game because it's an awesome game. For what it's worth, Thief 2 tones down the undead quite a lot (there's hardly any undead in the game at all) so you will likely enjoy that game more. But you really should finish the first game because the excellent story continues in the second, and you won't want to miss any of it.