Well, you can make changes - just like Schnipp did in that video...however, you need to create the actual .DDS file in something like Photoshop or GIMP or Paint.NET (I think all three support .DDS files, at least via a plugin). What is shown in the video is a simple rim color change and I would probably use this method only for simple color changes. Wings, Rims, Spoilers or other parts that I want to be solid colors. If I were going to make an actual skin with logos & sponsor stickers, numbers, etc. then I would bite the bullet and just do it the old fashioned way. In one of those applications I mentioned, create .DDS files and save them with the appropriate name in a new folder. I think all Kunos cars come with templates that can be used to help make the skin creation process do-able.
I've never created my own livery from start to finish, but I have modified a few and it is a bit of work...especially when you don't know what you're doing yet, like me.
If you were hoping that you can just move a slider to change colors, CM can't do that. At least, not yet. Who knows what the hell x4fab will come up with next. He's a mad scientist!
But, if you create the files in an image editor like Photoshop, let's just say for the doors. Then yes, you can just use CM to apply the new doors file you just created. I hope that answers your question...unfortunately, I don't know a lot about some of these newer features in CM. The program has changed so much since I first installed it. But, I think all of the changes have been for the better - maybe the 16384 x whatever ginormous screenshots were a little bit of overkill - he was just having some fun, I think.