Maybe this wasn't clear from my first answer, your not going to find where the grommet exits on the outside if your looking at the fire wall. It exits INSIDE the fender, in a space between the outer body and the engine bay cavity. The cable never enters the engine bay at all.
(photo from another thread when I did this)
The only way you can access the grommet from the outside is to remove the plastic that lines the front passenger wheel well and look near where the power antenna motor is.
With the
stock setup, the cable has to be replaced because there is no way to unplug it from the antenna, and it's shielded meaning you can't splice a new end on and get good results. Some aftermarket solutions allow you to remove the cable from the antenna. Hopefully yours was done this way.
The grommet is another interesting thing. You can only reuse it by cutting the old cable and sliding it off. There is a stopper along the cable to prevent too much cable from coming outside the vehicle, and on the other side there is a power antenna. Even if you managed to get it over the stopper, you'd still have the plug that wont fit through. There is no way around this, you have to cut the cable..
I managed to follow the stock cable route and use all the cable clips along the way. At a minimum you need to remove the glove box, the panel that the glove box light is attached to, and the whole center part (you have to remove this anyways to plug the new cable into the back of the radio). It doesn't require any special tools. It's doable, but it's difficult.