Yeah, in theory if you change one string at a time it doesn't mess up the tension of the neck. I do it that way and have REALLY dirty necks on my instruments - which I clean once a year.

Here's something that may be of interest. I use a dropped D tuning when I play in D or G or even A (believe Pete Seeger does the same) so I always replace the bass (6th) string with one of slightly heavier guage. I used to have my sets made for me by Labella, but now I get a custom set from "MasterClass" in Britain. I really like them. They run 12 to 58, but have a much lighter tension. (about the same as a med-light, but cuts down on buzzing so you can have the action pretty low.

Rick