The mechanics of shimming has always worried me, particularly with very expensive scopes.
If you look at the relative angles involved it could easily be possible to damage something.
Luckily my chosen discipline requires less slope to get on optical centre than the FT guys, but I still do it as carefully as I can.
I personally use Aluminium foil but in a way that the geometry is less harsh, I take a long strip of foil that is cut just shy of the width of the mount, I then start to fold this back and forth with each fold slightly longer than the last, the length of each depends on how thick you want the final shim.
This creates a shim that is profiled and more supportive, rather than one that not only shims up but reduces the mount diameter so much.
I also use a torque wrench for tightening down - this doesn't completely remove the danger of crimping but in my opinion does reduce it.
I think this shows what I mean:
Last time I did this I did work out how many MOA each fold gave but cannot remember what it was