You'll have to take off the pads from the driver, which exposes screws. You take out all the screws and separate the cup from the driver. Not completely as there's the cable but enough to remove the felt without damaging it, helps to put the headphones on the table when you split the driver and cup instead of holding it. The felt is on there by sticky tack completely around the edges and also the center ring where the spikes are. If you do it carefully you'll be able to remove the felt without ripping it and thus being able to reverse the mod should come time to go back to stock form. Hemipowered007 was able to fully reverse his but opted to go back to without the felt. You DO NOT want to remove the felt from the grill side as it's tucked under the cup.
If you think the HE4 sounds like the HD800, try it with the mod.