Z Axis Height Calibration

[PolkCountyMike]

What do you do when the correct you made is slightly more? My cube came out 20.04 ... do you adjust the already changed number? Or do you change the 0 by... 0.4? How would you solve this further dependency.

The adjustment should be to the already changed number as that is your new zero.  As for dependency, I assume you mean that your first adjustment overshot the target.  You might assume your first measurement was in error or you might average the results and change the zero by 0.02 instead of 0.04.  If your build plate is not perfectly level, the thickness will be influenced by location of the cube on the build plate, and the thickness may vary across the width of the cube.

So if I change the file to Z-1.16 at the start, but I overshot by .04, would I change the file to Z-1.12 or would I change the file to Z0.4 (to compensate?) ... how would I reset it back to default Z-axis?
Thanks!

Based on these numbers, you should change it to Z-1.12.  It is the same as saying instead of 1.16 mm short, your original cube was only 1.12 mm short.  I haven't done it, but to go back to the default you should be able to replace Z-1.16 with Z0 or just rerun your original gcode file before it was modified.