Can a 12-25 cogset be changed to 12-27 easily?

[rebeccaC]

I'd love to stay with Ultegra since I've already been adding weight to the bike with my new Mirrcycle road mirror and all the crap I carry in my seat bag, but if it makes a sizeable difference in cost, I'll go with 105.

Emily, according to specs there is only a 37g difference between your 12 25 and the 105 12 27. You might want to look at the price difference between an ultegra 11 28 and the 105 12 27, a quick look at a few places online shows it as 20+/-......in any case as Oak wrote you probably won't notice a difference in shifting between the two. I talked to a friend and she said removing your cheater brakes should just be a cable and housing change.