Step 0 - Do not omit this step! Back up your game!

Step 1: Make the changes you want to your Sim(s), in or out of game.

Step 2: If the game is running, save and close it.

Step 3: Delete Thumbnails folder (and any cache files visible).

Step 4: Start game.

Step 5: Pick a household, any household, and purchase Phaenoh's Phonebook.

Step 6: Have a household member look up a number. Page through the phonebook and verify that the thumbnails have been updated.

Step 7: Save the game (just for insurance).

(Step 8: More insurance - back the game up again.)

Why not regenerate the portraits of the specific people who were changed instead of all? You usually redress one or a few people at a time.

That works if you are changing Playables. When it comes to Townies, Downtownies, Dormies, Professors, etc., it's easier to use the Phonebook. (Especially if you have made changes and forgotten or neglected to update as you went.)

The Phonebook won't update Service Sims, just any and all Sims your Playables may have a reason to call up and talk to.

If you have Apartment Life, what is the purpose of this? They change their damn portrait thumbnails constantly in that game to the point I downloaded LazyDuchess's exe mod to nix it. (It doesn't work perfectly but it does cut it down a lot).

This is another partial counter to Apartment Life's annoying habit of constantly deleting (not just changing) portrait thumbnails. If you run this and then immediately save and close the game, you will be able to see what all your non-Service Sims look like. This is useful in case you want to do a bulk export of Sim thumbnails for any reason (making your own family trees, etc.), or just want to check your Sims out in SimPE.