[Reticularas]

Didn't expect to see this here.

I heard this rumor a long while ago (15+ years) while still in school. I did it to my headphones but learned that it pretty dramatically increased sound leakage. I'm not sure if was the exact same models of senns, but the trick has been around awhile.

[nailer]

Same here. Did it and got complaints about sound leakage from my colleagues.

[devnullbrain]

Don't buy open-backed headphones to use in a place with colleagues.

[cuvinny]

Yep, I read about this and did the mod on a pair of 555s back in the late aughts. I didn't notice a difference.