I used the plasti dipping window trim DIY on this forum for the basis of this process, however, that DIY was done on a coupe and the process for plasti dipping a sedan is a little different because if you dip the window trim while attached to the car on a sedan you will have an area of chrome that is visible when you open your doors and it won't look very good. So, after digging around on this website and others, I decided the best option would be to remove the upper piece of window trim and dip them while off the car and use the original DIY for plasti dipping window trim method for the lower pieces of trim.
I tackled the project this weekend and it wasn't that difficult at all. I started by opening both doors, removing the upper trim starting in the center between the two doors. You just pull it back toward you gently and start working your way to the rear of the trim and then back towards the front. I will tell you that when doing this the trim is held on by plastic clips and pieces of some of the clips broke off (i'm guessing just because my car is an '06 and plastic has hardened over time and weather). It worried me when I took them off after seeing this that they wouldn't go back on firmly, but they went back on as good as they were attached before I removed them so no worries there (at least on mine.)
After removing the top trim pieces I masked off around the lower window trim as it's outlined on the DIY on the forum leaving about an inch or so of exposed car body below the trim and I masked along the edge of the rubber at the window at the top side of the lower trim. I hung long pieces of newspaper below the lower tape to protect from overspray on the car. Over spray will come off the car but it takes some rubbing when it's only a thin speckled area of dip so mask as good as you can. I only had a couple areas I had to clean up and it wasn't a big deal at all.
***The most important part: After you've removed all your masking tape and newspapers and you begin removing the layer of dip that's below the trim that you sprayed on your actual car be sure to take an exacto razor blade and place it under the edge of the trim and cut along the length of the trim. This makes sure that when you pull the layer of dip from your car it DOES NOT get caught on the dip on the trim which can pull it up from the trim itself and make it ugly or need for a redo. When you use the razor blade it leaves clean break from the dip you pull up from the car and the dip that's on the trim. I learned this through trial and error as I screwed up the first side I did and had to redo it.
It was relatively easy. I've never masked anything before and it came out without a hitch. Let me know if you run into any problems if you decide to do this. I love the look it gave my car. It matches much better with my matte wheels, blacklines, tint, and black 330i badge.