If you use this cheat after you change the trait in CAS and return to live mode, your sim will stop getting the buffs from the old trait.
In order to cheat traits, you must first bring up the console by pressing Control + Shift + C. Do it all in one fluid motion with your keyboard. Playstation and Xbox players can do this by pressing all four shoulder buttons simultaneously.
Once the console (a white box in the upper left corner) is open, you can now type in commands.
Use traits.equip_trait TraitName to add a trait to your Sim, or
traits.remove_trait TraitName to remove them.
Note that if you have trouble getting one to work you can attempt to put trait_ before it, such as traits.equip_trait trait_DogLover.
Cheat found here: https://www.carls-sims-4-guide.com/traits/cheats.php
