2020 AM8 M3 t-nut easy installation

How do you put a nut into the slot of an existing project that has fasteners at both ends?
You take it apart. or...
I decided to add some small part to my printer, and didn't want to "undo" one end to slip the t-nuts in.
The solution is an M3 nut in a plastic holder that turns as you tighten it.
Don't use it where you need structural strength, it's to hold small stuff on afterwards, LEDs, filament guides,