auto outfit change for child sims

Hi,
I don't want to get into too many detail about the mod I'm creating but I'm having trouble creating a function. 
I'm trying to use the injector method to make child sims automatically change into a custom outfit but I want the change to occur a few days before they age up. Which function in Pycharm allows sims to change their outfit and retrieve a specific outfit? 

I can't be sure if its def change_outfit in outfit_tracker,  def change_outfit in sim commands or somewhere else. 

Thanks