you dont even need to primer the car let alone etch it... what colour is the car now? and what colour is it going to be?
people have this misconception that the car has to be primered to get painted but that is wrong. if the car is at metal or has bog then that needs to be primed to allow the paint to stick... etch primer is not even required to use on bare metal either, it is better to use but not absolutely necessary...
all that needs to be done is that the car needs to be rubbed back with 800grit paper to get all the clear off and pretty much get rid of a layer of paint... once thats doe depending on what colour it is and what your gonna paint depends on what you do next