Sadly, I don't know the details of what he was attempting; he was a bit closed about it (didn't want to spoil anything; I'm not playing in his game, but I know a bunch of people who are). And yeah, I would think that it might be fairly easy... dunno *shrug*.Interesting. It's not something I can say we are addressing specifically (and it's not something I hear as a common "complaint") but it shouldn't be that difficult to do. We will be providing charts that will let you modify a creature's "spine" quickly: BAB, saves, Hit Dice.
That said, is it really that difficult to do now? What type of creature are you looking to downgrade? If it's a specific ability you want to use, why not just give that ability to a less powerful creature?
Or even better, creature a "new" creature from scratch by just advancing the Hit Dice of the monster type (again, its Spine) to the level you want, slapping on the abilities you want it to have, and describing it in-game the same way you would the normal version. Your player's will never know the difference.