It's probably the second time I bought a headphone with a strong intention to mod it. I gave my new Alessandro MS-1i a couple days, then I started. My main intention was to get rid of internal reflections while not compromising openness. My first attempt was a piece of slightly felted synthetic wool. I used 0.6 grams of it on each side (the amount is a usual quantiy used in vented speaker enclosures, scaled down to the smaller cups). See how it looks inside:
And outside:
Black wool hides everything inside the cup - nice for looks.
I did not like the tonality of stuffed Grados at all. Bass was OK, but treble went completly wrong. It's hard to explain, it had to become less peaky, it probably did, but everything just got messed up. I have a little theory on this: music just isn't mixed to be listened in an anechoic chamber, our listening rooms produce lots of reflections and obviously sound peaky. Better headphones do replicate that effect (it's sometimes called "glare") and Grados are no exception. Cheaper plastic models are probably just tuned to sound not as good. We can't blame John for that, but we can try to change the sound for better.
The next iteration was simple, I just applied a piece of automotive dampening material to magnet cover, trying not to obstuct vents:
Not sure what it does to the sound, but it won't hurt.
I used a 6mm wide pen clip as a gauge in order to keep the housings even:

This configuration didn't last long. More mods have followed:

Let's see them in detail:
A minimalistic felt lining. Dark magenta is one of my favourite colors.
Vibration dampening material not only adds to weight, but also changes inner shape of the cup to soften possible resonances. The plastic stick behind the driver is a smartphone opener tool. I use it's sides to pry cups open.

These are L-cushion replicas from ebay. The smaller cushion can be fit under the bigger one for softer feel. I like the bowls for more open feeling and tamed bass response.
The above setup lasted for a week until I did the last mod:
Cup depth readjustment. The opener tool is 8mm wide, just 2mm more than the pen clip I used before, but the difference is about as huge as changing pads. Treble coloration is very different now: colder and more neutral. I highly recommend trying such readjustment to everybody. I haven't yet tried 7 or 9 mm clearance, but if you do you will get some interesting results as well.
Finally, I achieved the tonality I like with all the Grado benefits. Please see my new favourite:
BTW, I have also changed the headband assembly: the old SR-80 headband turned out to be slightly better: it has a nicer texture and softer feel.