Indeedy doody, Lucyfoos… memorize and memory... ahh, the features and gizmo's we waste our time coding for you peons...
Anyhows, no, you can't set cube codes. They're not really meant to be permenant residences, hence the reason they are in a hotel and not an apartment building. The lock codes aren't stored by the door in the case of cubes, the doors being 'dumb' terminals linked to a central door 'server'. Makes it easy for the hotel employees to deal with maintenance, unruly guests, roomservice (?) and other such daily routines that would be your own problem in an apartment. (Okay, forget room service, I have no intention of cleaning your stinking cubes...) Anyhow, that's why you can't set cube door codes. And yes... that -is- how it is coded, doors don't have -any- info about the door code stored on them but have a 'link' to a server object which has the power to over-ride all hotel doors, change codes, etc.
Technically this makes it harder for Joe Catburglar to break into your cube, since he can't combo hack the door... but, woe is the entire hotel if he manages to crack the door server and open every door in the hotel...