I think with the 1.03 patch they made a change to the multi-player save file. The method still works though.
My advice is to backup all your RDR saves first, then delete the multi-player save and the patch data/game data.
Then off course, don't install the patch and play in LAN mode all like before. When you got the desired rank and go back online your mp save should still be the way you left it.
So, multi-player wise, when doing this trick, you have to start over and create a new version 1 game multi-player save.