You can always temporarily play any sim, give them a job etc and then mark them as unplayed. But any unplayed sim in any world has the same percentage chance of the game pushing them into a job. As soon as any household/sim is marked as unplayed again the game may remove them from their career and push them into one of the needed NPC rolls (as MarianT said -mixologists, gardeners etc ) but that is just normal game mechanics. So really, MarianT answered your question perfectly.
The chances are pretty low for any sim in any world to be pushed into a career though so if you want any unplayed sim to have a particular career it is better to set it up for yourself.
