Yes, it is like a different headphone after the change, BUT there are many ways to do this. Some may yield little change and apparently some may degrade the sound. Mine are re cabled for dual entry, the cable are soldered directly to the driver terminals (the headband cable is no longer used, the mini XLR no longer used and multiple solders and cables inside the cans are no longer used). Simply plugging a new cable in place of the original one into the mini XLR may not bring about much change.
See post 2051 in this thread and some subsequent ones
Thanks for sharing this experience with us. It seems like a fun pair of phones to tweak with. I like your dual entry idea.