I recently had to do this on a project, and I thought I'd share how I did it.
I had a corridor wall on a 12 story building going all the up the building. This is great for coordination since I can be assured the my walls stack up the building. However, later on in the project, we had some clearance issues and decided to shrink the corridor down by 2" on just floors 7-12. The problem was, I didn't want to just pull the existing wall down to bottom of floor 7 because all of the doors, associated wall tags, dimensions, etc. for the floors above would be deleted.
Go into a wall section, and use the Split tool to split the wall at the location you want them to be different. This, however, brought up a separate issue where, for some reason, Revit locked the centerline of the two walls together and caused them to move together when I just wanted to move the top wall. Naturally, It took me a while to figure out that Revit had done this as I would move the wall on the upper floors, and then realize that the bottom floors were wrong (SURE WOULD BE NICE IF IT WOULD TELL US THAT IT'S GONNA LOCK THE WALLS TOGETHER RIGHT?).
Again, I didn't want to do anything drastic that would cause the inserts and annotations to be deleted, so I had to figure out a way to move it. I couldn't see a padlock or anything when I selected the walls that would show me they were locked (Revit 2010).
So, what I did, was pin the lower wall in place, and moved the upper wall. When I did this, it gave me the error to remove constraints, which I gladly accepted and moved on with life.
I hope this helps.