Modding can be very rewarding. I have modded my Sennheiser HD600s to remove the veil and expand the soundstage. Trekasaurus has modded his HD800s and is in the process of having his IE800s modded to solve the cable problem that those headphones have. Many HiFiMan HE-6 (and many other HiFiMan headphone) owners have modded their headphones, including Trekasaurus. MrSpeakers and ZMF got their start as modders before they moved onto fully building and designing their own headphones.
Beyond modifying headphones. Some of us on this blog have experience with DIY amps that absolutely make headphones sing like angelic choruses perched above your dreaming ears. In this section we post our experiences with modding and DIY builds. Hopefully, our audience will find this information illuminating.