Finally got around to modding my Meze 99 Classics today. I am very happy with the results.
I was never happy with the sound since I had purchased them, but loved the looks, comfort, and how easy they are to drive. The part I hated was that the bass bled into the mids with the newer larger earpads. It was a complete disappointment from all the positive reviews I had read which referenced an older earpad design. So they just sat for a few months.
Today, I opened them up. The bass port on the back of the drivers were wide open. I cut round discs of masking tape to cover each of the the bass port holes on the back of each driver. I experimented some, but came away with using a hole size of a T3 hex bit for the new size of the bass port. This essentially made the bass port holes about 25% smaller. The result was still having the fun punching bass, but reduced the bleed over. They now sound like I thought they should have sounded like. FYI, in case anyone else wants to experiment with a completely reversible mod.