If the items that you see when you are copying a layout, look like Sanso 1920x1080, those can be found in the root of the Everquest folder.
Look for the files that start with UI_ (example; UI_Sanso.ini). Just delete the ones that you no longer want.
They would have to go into the specific UI_charactername_server.ini file and delete the many entries for those specific resolutions. There is only one file which holds all the different resolutions.
The simplest solution is actually to make a new character. Log onto that character and do the /copylayout command choosing with all the options checked for the specific resolution you want to have. Next, delete the original character's UI_charactername_server.ini file. Log onto the original character and /copylayout of the new character. Now your original character should have only the resolution that you want them to have. If you want more of them then /copylayout for each of those as well.
Xianzu 95 Monk Tunare
Bearer of the Shackle of Tynnonium
Wielder of the Whistling Fists
Ascendant Apostle of the Celestial Fists