Yup, that’s it. Remove the shock, unscrew the air can (was easy to do by hand on mine), clean the main seal, apply a thin film of suspension grease e.g. slick honey, screw can back on (you need to push it firmly whilst twisting), bolt the shock back on, set your sag (probably will now require a lower pressure), job done!
Let us know if you find it makes a difference or not.
I would be a little bit dubious of following that negative air bleeding advice, the negative spring is supposed to have air in it, for at least balancing the preload inherent in an air spring. And if you look later in that MTBR thread, the speci tech says so himself
The negative air pressure plays a big role in minimizing top out. Bleeding out the negative pressure will allow the shock to top out harshly. The improvement in small bump compliance was due to greasing the air sleeve seal, build the shock without bleeding out the negative air pressure and this will improve small bump compliance even more, as the other job of the negative air spring is small bump compliance.