Hi @cbramley,
Thanks for asking this here! 
May I ask why you’d need this? I might not see the full picture here, but for me it seems to be a bad idea to increment it on some branches but not on others.
You’re referring to the BITRISE_BUILD_NUMBER by build counter right?
One of the most important factor of the BITRISE_BUILD_NUMBER is that it’s the same value as the one you can see on bitrise.io
Not incrementing it would result lots of duplicate build numbers on the UI.
If you can clarify a bit what the use case for this would be we can provide more info. From what you wrote I think you might be interested in this discussion:
In any case, if you have any questions we’re always happy to answer here! 