Not completly sure about this but i think EQ2 checks its folders on startup and replaces modified ones. You have to setup a new custom folder below the UI Folder and extract your files there. After that you have to tell EQ2 where to find your new stuff. Please check any of the custom UIs Readme how to do that.
Im not good enough to post a real HowTo here, just to give you some hints where to check and what to do.
And please excuse my bad english
Greetings
Karkoris / Slurp
Valor