I do know that you need a special needle to insert to fill with gas.
I spoke with a friend who does alot of suspension work and he drills and taps for a schrader valve so it makes adding the gas more universial.
I just took apart my shock last week (first time), and changed the fluid. It's really easy, no special tools needed (other than the needle, gas, and regulator to charge the reservoir). It's like any other shock. The only tricky bit is to make sure you set the piston height/depth to where it was upon disassembly. Bleeding the shock is like any other.
I took a few photos when I did mine, so I could write something up if you're interested. I also measured piston depth if somehow that is lost.
I am the second owner of the bike, but the first owner kind of hacked up the shock. I am not sure how that happened as they are quite easy to work on.
An ohlins shock workshop manual showing complete disassembly and reassembly can be found at : (do right click "save link as" - it is almost 5 megs so be patient).