This is very easily done with a snippet and your own custom snippet class since basic_extras is a list that can be modified at runtime with no problem.
I've attached an example for you to take a look at. It injects a loot into the brush teeth interaction so the sim gets a buff named TEST.
If you extract the .zip file's contents directly into your mods folder (leaving the folder structure inside the .zip file intact) the script will run without needing to be compiled, allowing you to quickly test out changes in the game without needing to compile to .ts4script every time.
Remember to rename the snippet class and the .py file to something unique to your mod.
In the snippet's tuning file in the .package, m= the filename of the file with the snippet class, and the c= your snippet class's name.