hello Tim,
first of all i am a Little bit "confused", because you are talking about DIY saw and bits. i may depend on my bad bavarian english,
but by a saw i understand somithing to cut with saw blades, but i my be wrong.
if we are talking about "clasic" mill or route with bit's there are a couple of differen way's for the Z Zero hight.
i do not know how you have to Change your bits (some Pictures would be helpful).
ok short description what is possible:
if your Tools can be placed into machine reproduciable (by bitholders) you can work with different tool (T1-T255), here the toollenght
Needs to be measured one time for each tool, and the a G43 Hxx (xx is toolnumber) will set the correct height.
if you have to Change (clamp) tool each time new your tool height setter Comes into the race. with a custom M6 macro you can
measure new tool lenght after each toolchange via your Setting plate.