There is a way to do this automatically. Use
www.fastjp.com and specify change at: BHM (or wherever), choose additional interchange time as a negative figure (which is then taken away from the minimum interchange time). It will generate invalid itineraries with reduced interchange times (these are labelled as such).
e.g. changing at BHM with a figure of -6 would give you connections of 6 minutes (12-6) or greater.
A few members of this forum know of a planner who tried his best to ensure passengers had the smoothest possible connections at York. Unfortunately his job went to Milton Keynes (and not many people are going to want to move there from York). Anyway he is very keen to tell us of occasions when his good work has since been undone by newer, less experienced planners; from my understanding there are quite a few of these.