The service center drills out the old bolt and puts a new bolt assembly with a special Campy tool. On the exploded view it is written that it has to be changed by service center.
You could always use the titanium bolt from 2009-2010 SR and then you could put it back together with C-clip. You will gain some weight though. Some aftermarket companies also make one piece bolt in aluminum.
The full procedure is to also check that after fitting the new bolt, the RD is actually perpendicular (within the tolerance) to the bolt - this in done with a stud bolted into a surface plate that allows the RD to be mounted, with the pivot bolt accurately at 90 degrees to the surface of the surface plate - the RD is then rotated about the pivot bolt and the distance from the surface plate to the tip of the cage is checked at several points to establish that the surface plate and the locus of the cage are co-planar.
Re-using the bolt as suggested in the thread referenced above risks several problems including later failure of the bolt and the fact that the bolt may distort, leading to the lack of co-planar movement and poor shifting ... the SCs are also generally in the position to use oversize o-rings to correct any "slop" that may have developed as a result of wear and tear and will do this as part of any replacement process.
Certainly in the case of SR, given the cost of a derailleur and the possible adverse consequences of a bolt failure, I'd advise getting a SC to do the job and do it correctly. I'm all for people looking at how to work on anything, bicycles, cars, aeroplanes, whatever, themselves - but there really are some jobs that it's advisable, unless you have all the information and all the tools / possible spare parts that you *might* need, to leave to those that are in a position to do the job "by the book" ...