Furthermore, the delicate generator mechanism housed within the hub body must be re-calibrated to tolerances of less than a millimetre each time bearings are replaced.
Haven't done it myself, but assume, that 1mm tolerance refers to the position of the axle and the shell. It shouldn't be too hard to check that there's for example 5mm of axle coming out of both sides of the hub and not 4,5mm and 5,5mm.
But... What about
From the link @PhilDAS posted last page?