Mike,
If you want to do it across the board, then sure go through the trouble. With DSM's we can change a single gear ratio instead of the whole final drive in order to achieve what your trying to think about.

Have you even driven a DSM with an evo 3 gearset, and you want to go shorter??? Oh yes right, I forgot you haven't driven a DSM in what, over 10 years!

No wonder your thinking about going shorter than an evo3 gearset. I'm at work too, but I figured this out and already did the math a long long time ago

DSM transmission crap is worthless and obsolete inventory now. Your trying to think something that Shep, TRE, or Jacks would have offered a decade ago, if we did not have such things as evo3 gearsets, and 91+ intermediate shafts which make it easier to change a single gear ratio instead of the complete final drive.

With my Evo X, there is no option to change a single gear ratio, so If I wanted taller or shorter gears, then yes I could easily swap the complete final drive. Although you can, you do not need to do this with a DSM trans.