As Paul says, no need to touch the adjustment of the verniers, but there is the possibility the exact TDC position will be lost when undoing the bottom crank pulley bolt, as the cambelt lower pulley is a lousy fit on the crankshaft, unless it's been shimmed to fit. I've had it both ways, so I recheck the precise timing (my OCD) but real world difference to engine performance maybe is negligible. Malcolm