I have a similar need to change the way Revit is applying area rules to specific areas.
In South Africa we need to measure Coverage and Floor Area Ratio both on the exterior face of the building. I could use the Gross Building Area scheme but then I cannot select Major Vertical Penetration to subtract that area for double volume areas above, plus we also measure GBA differently to FAR. So either way I have to create additional Area Schemes and manually draw each line individually, effectively making the "Rules" set by each scheme totally useless to me.
It would help so much if I could just set the rules for each Area Type in a Scheme individually.
Furthermore, we also have to calculate the internal floor area separately to determine our Fenestration Limits, so I inevitably end up making 3 or 4 different area schemes and having to manually draw each individual line as Area Boundary. This process is killing a lot of time for me.