okay, cool, so then just do it. Anything a regular user can do, root can do.
You do not actually want to use the root account like that though.
What you're really asking, I think, is how to get two users to be able to work on the same files in a dir.
root <-- don't use this.
uesr1 <-- cool.
user2 <-- okay, cool.
make the users members of the same group and give the files/dir group ownership. put ug+rw on the files and ug+rwx on the dirs.