how to have several GUIs in startup raspberry

i have several user interfaces(GUI) with different access levels in my project..in some of these GUIs, the user can determine which user interface should run in startup raspberry next time. now, in your oponions, should i write the code of all GUIs in a single code or several codes? it is supposed i write all GUIs in a several codes… how will the selected code by user be run in startup raspberry? i don’t really know how i do it…. thank you