I did this a while back on dreamwidth and it took me 2 rename codes and three journals to accomplish, like how you described in the last question you asked. Also you would have to make sure that you don't have username 1 redirect to username 2 as it has to be available to be renamed to.
Details: I had OLDNAME as my main journal but I wanted my new main journal to be NEWNAME. I didn't want OLDNAME redirecting to NEWNAME but I wanted all my communities and friends from ODLNAME to be moved to NEWNAME. I renamed OLDNAME to NEWNAME, and checked to option to transfer friends and communities, but did not check to option to have the un itself redirect. I then created a brand new journal and renamed it OLDNAME. So now I have both OLDNAME and NEWNAME in my possession. NEWNAME is my main journal with all my posts, friends and communities from OLDNAME.