An easy way to home Z is to just put the GCODE that Ryan provides on the sales page for for his touchplate in a file with a .gcode extension on your SD card. Then you can just run this file like any other GCODE file to home your bit. I recently upgraded my Marlin and found that Ryan had provided a custom menu item to home Z, so you may also get this custom menu if you update the firmware for your Ramps board. Neither solution will disturb your old files.
As for bit changes, here is a recent thread on the issue, and I’m sure there are many more on the forum. There is not a one-size-fits all solution: