setting BTTMenuItemText via the update_menu_item function is just a temporary override. You can not change it via the UI.
// edit: ahh I forgot there are now ways to actually make this persist. In that case you are right, there is currently no way to edit it via the UI anymore. I'll think about this! Probably it should just reset when changing the attributed text in the editor - I'll add this with the next alpha.
In case you want to edit attributed text using scripts, you can now use HTML when setting BTTMenuAttributedText. (Can a floating menu display live network configuration? - #2 by Andreas_Hegenberg )