they are removable, if you see zeo's video, he also says that you can remove them, I took them off by using a butter knife along the edge, trying not to break any of the clips inside
here is the back side of the earpad, it has five holes, four for the clips and one to make sure its the right side...
something like this has been shown before but this is how they look like with HM5 pads on (the extra thick ones with memory foam)
in my opinion they give the headphone a bit more bass, but closes you off making them sound more like closed headphones than open ones, (e.g. there is more isolation for you but not for those around you), its also much more comfortable (biased opinion) but have a bit more clamp force because of the added pad thickness, my ears no longer rub on the inside of the headphones
zeos and others sugest using a 3d printed ring, more to protect the earpads from the clips
I haven't used them, probably since I was dissuaded by other opinions saying that these pads wouldn't be so good for this headphones, I kinda disagree, but didn't think I would keep them like this for long
Even zeos doesn't think that the change is as good as putting HM5 pads on hifiman he-400s (in his review of his modded shp9500)
edit* also even thought the earpads are removable, I haven't seen anyone selling replacement pads for them anywhere