The Deore M591 sits more inboard on the bike, and the cable enters the derailleur from a different point (closer to the top I think), so the cable between the frame and the derailleur doesn't need to be so long. I cut a little out of the housing that runs between the derailleur and the frame. If you're reinstalling the OEM derailleur with a new cable, you don't need to cut the housing.
If you are removing the derailleur, you can either pop the chain, or sometimes you can dissemble the derailleur cage.