Behind the baffle
The design of MDR-1R's acoustic vent is rather simple. It consists of a rectangular-shaped opening, which is damped by a porous nylon mesh, and a small undamped hole.
I do not recommend tempering with these vents, as they are there for a good reason: sub-bass equalization. Unless you are familiar with designing an acoustic low-pass filter, don't even bother to touch these.
In front of the baffle
Since MDR-1R's ear pad is proprietary, third-party pads can't be used. A piece of foam may be utilized behind the ear pads to damp the mid range. And in order to decrease the mid-range hump, an annular-shaped foam padding can be sandwiched between the ear pad and the pad mesh to increase the distance between the user's ear and the driver.
The annular padding not only damps the mid-range, but also should help tame the peak at 10 kHz. Blocking the frontal baffle vents amplifies the mid-bass range up to 5 dB.
Inside of the baffle
Unlike the classic CD-series, of which a dense damping material has been incorporated by the manufacturer, there is nothing behind the driver of MDR-1R.
While I really like the second one, since the goal I've been assigned is to decrease the mid-range hump, the design has to further improve.