Ultravixen - there are a number of ways to achieve this, I will detail one that doesn't use InSImenator in case you Have Free Time - just keep in mind there are probably numerous other ways - I am only going to detail one of them.
Requires: Merola's Mind-control Mirror from here:
http://www.simchaotics.net/Files/MerolaSims2/MindControlMirror.htmAFAIK works in all game versions
Have a Sim go shopping to purchase the outfits you want to use so they are in the clothing catalogue for that family
The NPC is on the lot, you use Merol'a Mind-control mirror and take control of the NPC (may cause issues with some NPCs since they are "incomplete" -- e.g., the school bus driver, taxi driver, death, etc)
Have the NPC use any wardrobe, chest of drawers, locker, etc to "plan outfit" and assign the clothing for the various clothing categories
Have the NPC use a normal mirror to alter appearance (hair, make-up, glasses, jewellerey, etc)
click on a family member and the NPC should revert to non-family status.