Stacking same buffs you mean? For example like two Inner Fires? I suggest base each buffs into different kinds of buffs just to make sure to avoid conflicts then rename those buffs to what you want.
Example, create 3 buffs with different basis or you based it into 3 different kind of buffs. Now change the buffs's name and properties you want (Might, Shield, Regen). There! Buffs actually I do know has no effects such as +damage or stats of its own and is only dependent on the skill casted so if you want to add effects, I suggest trigger it that if he unit has these buffs, add either damage, armor, stats and etc. it depends on you.
It only replaces buffs if they are same I do think. Try searching also because there are actually same problem as yours which is solved.