Aslong as you do the car the correct way you shouldnt have any problems..If you do it the "notches" way by taking the trailing arms off the beam, re-positioning them to the desired height then putting them back on, chances are you will have problems..The seal on the bearings wont re-seal correctly, water will get into them and destroy your whole Axle..You could do it this way if you were going to replace the bearings at the same time, that would be fine..
If you do it the correct way, by removing the torsion bar's, not the trailing arm's you wont have any issues whatsoever..
Most garages do it the wrong way, by removing the trailing arms, this happened to me and when i stripped my axle down i found that my bearings were totally dry and were almost knackered..Eventually my axle did die though despite re greasing the bearings, i didnt realise at the time that once you break the seal between the trailing arms and bearings it will never re-seal properly..
If you take it to a garage to have it done, supply them with new bearings and ask them to fit those aswell, everything should be ok then although that method still isn't really ideal as it doesn't allow for accurate lowering..
Hope this helps!