That's what I do anyways. I like to up the farms in castles ASAP that I have designated as troop producing provinces. That way I get the good stuff earlier.

Lately I've been flirting with the idea of convertion large cities early on so that I get better troops sooner. For example, as France I've converted Paris into a castle and then quickly into a fortress, which has scored me good cavalry, infantry, and artillery earlier than other factions who kept the cities as they were.

I know that as Germany the best use of Bologna in Italy is as a castle and then quickly a fortress. Bologna is constantly being attacked, so being able to produce feudal foot knights early and take the offensive is great.