Not exactly. Besides retaining silly uniforms on community lots after college, mascots personality and behaviours are retained and uneditable.
Such as days left in age, I know. There's ways around that though.
Knocking up female NPCs corrupts their character file. At least so I've read. Unless you've made them selectable and keep them on the lot for the duration of the pregnancy.
In fact you can't get an uncontrollable Sim pregnant. If somehow you do, it won't corrupt their character file (unless you are messing with uninteractables such as the hula zombie), but the pregnancy will go wrong. I was referring to former NPCs.
Beat me with a stupid stick if you like, but I don't know what that means.
No traversal costs means their needs do not go down from walking as it does for all other Sims. This is most noticable on the huge lots: send a normal Sim and a former NPC from corner of the lot to the other, if all other things (personality, asp, starting needs) are equal the normal Sim will have significantly more needs decay than the former NPC.
(…)Had I had that first sim propose the move in to her mascot lover while she was still at college, there would have been no problems.
I did the proposing unto engagement in college. It gives a nice bonus for graduation party scores.