I am removing a section of drywall and replacing it with some rockboard
(durock, hardibacker, etc.)

Can I just cut the existing drywall flush with the existing stud, then add a
second "stud" by attatching it to the existing stud (with fasteners), and
then attaching the rockboard to that new "stud"?

Here's a picture of what I tried to explain:

http://img266.imageshack.us/img266/1923/drywall.jpg

Seems like it would be a lot easier than trying to cut the existing drywall
down the middle of the stud.

Whad'ya think?

Jon