UnleashX doesn't undo any edits on booting. When you change the skin, the first time you press A it loads the new skin in memory, but DOESN'T change config.xml to point to the new skin location. Thus when you reboot it still loads the original skin - no undoing of edits required, because nothing was edited in the first place. Config.xml is only rewritten if you press A twice - the first time loads the skin into memory, the second time commits it to config.xml.
Apart from the default skins that are embedded in UnleashX, every UnleashX skin publishes its skin.xml, and they are all editable. There are hundreds you can examine here
As far as skinning guides, try searching here on Xbox Scene for UnleashX skinning guide. I can't find a single resource that pulls it all together, but the nearest I can find is useful posts like this