I used to do the following. For a full UI reload do
/loadui <UI_folder_name>
followed by either a
/quit <character_name>
or a simple
/load_uisettings <settings_file_name>
depending on whether dynamic data and hardcoded window pieces were involved.
However I did not do a full UI reload usually, instead I did a lot of runtime modding, e.g. I moved a UI element around via UIscript while in game if I needed to get a location exactly right, or I moved it by hand and then queried the location via script, stuff like that (in ProfitUI the control center has a text box where you can enter UIscript - the login screen has a hidden one too which I used for stuff that did not even require a logged in character, faster that way). Only once that was done I would modify the XML accordingly and do a full reload to double check. Quite a few changes I only did to the XML without ever being in game as well.
PS: also always log in via the everquest2.exe instead of the launcher, does not really take long that way.