The problem with changing things directly relating to a modelīs statline is that it should also affect the cost of a model (e.g. a youngblood will get significantly worse, is 10 GC a fair new price?) and if you go down that route your are opening a whole new can of worms. If you use other houserules like different shield or parry rules that is less of a problem, as all warbands can benefit from it simply by buying the right stuff.
Because of this i prefer RationalLemmings suggestion of using WS in a parry, that is less intrusive.