lol funny I have the same issue with my littlest one. She likes default and doesn't want all the ge-wiz stuff ATM. Basically you are stuck with doing the following:
- /load_ui <ui_name> or pick form the list.
- /load_uisettings <setting_name> or pick from the list.
There are many issues with doing this; the chief ones for me is group member names never get repopulated. There are several more.
Like gm9 said, there needs to be a eq2ui_skininfo.xml in the custom folder for it to show up on the list. There doesn't have to be one if you do /loadui <ui_name> though.