Yes, my avatar are the reshelled ER-4's.
My reshelled ER-4S has a different sonic signature compared to the normal ER-4S and it's because I changed the resistor from the stock ones to Vishay Z201's. At first, Rooth used a chip resistor which wasn't the stock one and the sound was dry, harsh and lacked 3-dimentionality so I sent it back and had the resistors replaced. Now they sound smooth and 3-dimentional. Personally, I think it sounds more smooth even compared to the stock ER-4S with the triple flange tip.
As for a reshelled ER-4S using the stock resistor, my friend on twitter has it and says that it sounds a bit brighter and thinner compared to the stock ER-4. He assumes that the hard material used for the shell contribute to the difference in tonality. However, if you like the sound of the ER-4, you'll probably like the sound of the reshelled ER-4 even if it does sound rather thin. My friend loves it.
The filters are placed quite deep inside the sound tube after reshelling so I have to send it to Rooth to have them replaced. I'm planning on asking them to put the filter at the end of the tube like the stock ER-4 so it can be replaced easily.