Yeah totally understand this can be a lot of work. SSH'ing and using gcode commands is exactly what I wouldn't want users to have to do haha...not the most intuitive or easiest for probably the vast majority of people. If Ultituner had a method to just jog the head left, right, up/down, and readout the current position that would be amazing.
In terms of the XY offset data...AFAIK you can currently override it manually on the touchscreen...it's just in a weird unitless value...but each unit is 73um from what support has told me. It would obviously be easier if your tool could read/write these values in mm, but not strictly necessary given the current touchscreen interface ability.
Understand your comment on the tool possibly being obsolete after a firmware change though. I'm actually surprised that the Ultimakers don't let you jog the head...almost every other printer lets you do this.