Changing a vanilla class tick()

I'm looking for advice and opinions on changing a vanilla class's tick() method.  I'm still pretty new to modding, and my Java is rusty (and wasn't great to begin with).  I used reflection in tickStart() and tickEnd() to set/reset some fields in the Village class to effectively change the (hard-coded) Iron Golem:Villager ratio.  I feel kind of dirty about it.  Is this a common practice or something that should be used sparingly or not at all?  Is there another or better way to do this kind of thing?