So, the first mod attempt at T20-mk2.
Put on an Beyer gel earpad. Only the left one so far. Really not easy to put on, very small lips, very hard to stretch and diameter just a little less than larger axis of Fostex cups. Took four attempts to put on!
First attempt was to fold the lips backwards over the earpad, press the pad against the cup and roll them over the cup. Unsuccessful, was only able to put about 50%.
Second attempt was pretty much the same, maybe up to 70%. Noticed that the lips got stretched somewhat.
Third time, I heated the pad by placing it on a radiator. They're much more stretchable when they are hot indeed. Still, maybe about 85% coverage.
Fourth time, I decided to stretch it manually. Get a hold of the lip and base/lip seam with one hand, and the same with another hand 1 cm away, then pull your hands apart. It does stretch a little! Then move to the next cm. Made it around the whole pad that way, and finally managed to get it on, had to even use teeth to pull the last bit. I think it would be best done with four hands and having some non-sharp tweezers to put on last bits of the earpad. Left the pad on 'phone to stretch. My fingers ache now, so I won't put the second pad on today.
Sonicwise, it's hard to say. My T20s are otherwise totally stock now, I thought they would be badly sounding, but they're not, at least to me. Surely, however, they are very dark, with emphasis on bass and good bass detail, and so low in highs that woman voices sound as if they all have running nose. Of course, it's not very efficient to compare that way, but some things are obvious. Mids and bass are reduced on Beyers - perceived volume is lower on them and imaging is shifted to other side. However, highs are brought into existence - some stuff is now only heard on Beyer ear, which was completely unnoticeable on stock. Plus the very deepest bass rumble, more felt than heard, appears only on Beyer ear.
Of course, that is hardly any useful information, besides putting them on. Will mod properly on holidays and listen to.