My b2evolution Version: 0.9.x

Hello. We have an older installation of b2evo that we've customized quite a bit. Currently we run 15 separate blogs out of the one DB.
One of our users has requested an additional field in the back office and I was wondering if anyone had any advice on how to accomplish this...also here's another twist, we only need the additional field on 2 of the 15 blogs. Thank you much. :)