If you wanted to rewire them yourself it is not very hard and does not require expensive specialized tools( soldering iron, solder, wire, plug). Beyers are pretty simple to disassemble and work on.
Removing the old cable - You would have access to all the wires once you pop off the clip-ring behind the left earpad. From there desolder the wires and then pull the old cable back out the preexisting hole in the ear cup. The little seal/gromit where the old cable enters the ear cup was glued to the cable on my dt770 but it separated with a good tug(I backed the cable up and separated the gromit outside of the earcup just as a precaution so that it didn't send the headphones flying when it did separate).
Assemble the new cable - You can go a million different ways with making your own cable. Some people buy wire that has all 4 wires already wrapped up and all you have to do is strip the ends and solder the plug on. Others go all out and buy individual wires, sleeve them with paracord and braid them up in all sorts of
crazy ways.
Attach the new - If you can fit the original gromit from the stock cable on it may save some time, be sure to put it on the cable before you solder. Match up the wires and solder the new ones on. Slide the gromit back in to place if it fits, if not you can use what ever material you have access to to fill the hole so it looks good from the outside. On the inside put a dab of hot glue where the wire feeds through the cup to hold it in place, you can use glue or blutack to seal any remaining gaps.
thats about it... other tools that make it simpler are wire holder for soldering(
helping hands) and a
cheap multimeter to check your wires
link to the cable gallery if you haven't checked it out
