I've read that the pro templates have a high bitrate but are confined to the H.264 codec. I'm wanting to select my codec and not be confined to H.264 as I will use these files in other projects with Apple Pro Res files and do not wish to transcode them.

In your screencast using Windows, when exporting from Lightroom, you have a choice selected for .mp4. This is not appearing on Mac.

Is it possible to add to the pro templates the ability to choose the codec from any of the codec settings installed on the Mac by tapping into the Quicktime export functionality?

No, Lightroom will only export MP4. If you want other codecs, you'll have to use the After Effects Workflow.