Some codecs have settings and some don't. If you pick one off of the list that has settings, you will have more success at changing parameters.
First things first. Does your list of codecs look something like this? If so, select the appropriate codec for your needs and see if it has options. None of the Quicktime exports has the option of changing from CBR to VBR as far as I can tell and to be honest I don't know which is being used. You didn't say if you were on a Mac or a PC but if you are on a PC you might consider using an H.264 export instead.
In this case, QuickTime is not the best choice. Use the standard MP4 container instead.
I'm having the same problem but on a Mac. I'm on OS 10.10.3 and running CC 2014.2.
No matter which setting I choose, "Codec Settings" is unavailable. I've been able to click and adjust in the past. Why not anymore? This happens in both Premiere and After Effects. I thought it was an issue with QT plugins but the fact I can render out to ProRes means I should be able to access the advanced settings, right?