I unlidded my Opty 165 this weekend. Apart from a small cut on my finger it went pretty smoothly. One thing to consider though, is that the razorblade you use needs to be fairly thin. I would guess the one I used was 0.5 mm or less.
Also, I am using a Zalman CNPS7700AlCu heatsink on the CPU. In its stock configuration it doesn't seat on the die with any significant amount of force so the HSF recommendation on that one could use a little footnote. What I did was the following: There's a sort of higher level that the retention bracket can sit on. I simply placed the bracket at the higher level (i.e. greater distance from mobo to bracket) and then was able to apply a good amount of force to the die using the two original mounting screws. I doubt that the higher level was designed for this particular use, but it works out nicely anyways.
All that being said, my Opty runs hot as hell. At stock speeds, after unlidding it, the load temp is 60C. I had originally tried reseating the HSF with the IHS still in place in order to lower the temps. When this didn't work, out of frustration, I decided to unlid the thing. I have only seated the HSF once after unlidding it. Perhaps it is not quite sitting properly. I guess i'll have to open it back up and try again.