So, I'm working on this mod right now, and when I load it with the game the game mostly works. The problem is, without my mod the game doesn't work at all anymore. I hypothesize that this is because I changed some vanilla scripts slightly. I was wondering if there is a practical way to "revert all vanilla scripts to default" or something.

You can simply uninstall/reinstall the creation kit. this should revert all scripts sources to their original form.
however you may have to manually delete all Pex files

Use http://en.wikipedia.org/wiki/Revision_control: http://mercurial.selenic.com/ (http://tortoisehg.bitbucket.org/), http://git-scm.com/ (http://kylecordes.com/2010/git-gui-client-windows), http://subversion.apache.org/ (http://tortoisesvn.net/).

Some valuable links ...
Overall: http://www.ericsink.com/scm/source_control.html
HG: http://hginit.com/
Git: http://stackoverflow.com/questions/315911/git-for-beginners-the-definitive-practical-guide