I know this is probably covered somewhere but I cannot seem to find the answer.  Once I set the software with the touch off for x, y and z, can I change bits and just zero the z-axis and not have to re-zero the x and y axis even though the bit size is different?  I am assuming that the axis are set for bit center rather than outside so I'm thinking that the actual bit size (assuming that the tools are similar to each other versus an endmill and v-bit). 

I'm re-zeroing the work every time I change a bit.  Can I eliminate the x and y and just zero the z-axis?

As long as you have set the centre line of the cutter to the edge of the work in X & Y then they will not change from tool to tool only the Z changes