You don't need to run Staredit/Campaign Editor to use GUEdit.
If you want to use it, you run GUEdit.jar.
When you load it up, it has some selectable options and some non-selectable (the ones grayed-out). One of them is "load".
Click on load and choose the .scm or .scx file you want to modify.
I think you need version 3.2 or later to have instant upgrades...