FYI, significant changes to the car setup system have been made in patch 3.0.
This means, that the SAVE OVER EXISTING SETUP feature only works with newly created car setups!
To make sure that everything is working as intended, please delete your pre-patch setups and create new ones.
Set-ups location on PC: C:\Users\YOUR NAME\Documents\Project CARS 2\savegame\YOUR ID\project cars 2\tuningsetups