Hi Honesty!
The classic concern with coldsetting a rear triangle -- besides making sure each side is set evenly -- involves getting the dropouts parallel, and this step is often overlooked when coldsetting to much wider spacing.
Most *hubs* seem to tolerate OLN differences of about 2.5-3.0mm difference overall, depending on chainstay length. Thorn use this to advantage on their Mk3 Audax frames, which are spaced with the dropouts parallel at 133mm OLN when the frame is built in the fixture. This allows the same frame to accommodate both 130mm and 135mm hubs by temporary spreading or compression with the wheel in place.
Going much beyond that *without* resetting the dropouts to parallel can sometimes compromise hub life, again depending on 'stay length (worse with really short chainstays, not so much with long ones). What happens is the dropouts approach the hub locknuts at an angle and when the q/r is tightened, the axle can bend slightly, putting the hub cones at a cant and leading to early bearing wear. I have seen axle breakage occur on occasion in such circumstances, but only on ramped dropouts where the q/r had to be set really tight to prevent the wheel cocking in the drops and where the cold-setting was pretty severe -- in one case from 120mm to 130mm OLN. I've not seen it happen with vertical dropouts, where q/r forces can be lower, and the problem could have been avoided entirely if the dropouts had been reset to parallel after coldsetting to the much wider OLN spacing. See:
http://www.parktool.com/blog/repair-help/dropout-alignment-ffg-2Just a data point or two for consideration and the reasoning behind the general concerns. If 't'were me, I would first check with Thorn/SJS Cycles to see if coldsetting would void the frame warranty.
Best,
Dan.