Moving entire users folders can cause all sorts of issues and is usually best avoided. Much better to simply move the media folders - Music, Videos, Pictures, Documents etc.
As for the mod, I find it worrying it feels the need to junk up your appdata with almost 4GB of crap. Perhaps there is a setting you can change for that particular mod to have it put the files somewhere less retarded?
Windows doesn't give you much in the way of customizing where system folders belong, and to be honest there is rarely much of a need to change it.
Rather than trying to butcher Windows to work around the space issue, work out what is causing the space issue in the first place and butcher that!