Type changes are passed onto the tower so they can ensure their conditional clearances are accurate, and I think some stands can't take certain types? Maybe someone who can see planes at their place of work can answer that one.
A good point there tc atco. The stand allocation system at my airport works off flight plan data. There are a number of stands that will fit a B735 but not a B738 or a B762 has turned out to be a B763 and a hasty call to airfield ops has had to be made before the back of stand road gets blocked by a stuck out rear!