Maybe I am not understanding what you are saying but if you open a part in the parts editor and go the metadata tab and make sure each part has the same family name and a different variant name you do get a part with different variants in the inspector under the variant field. Or at least when I have added to an existing family like the ESP8266 it has shown up in the variant field. I also used a test point as the base to create exposed copper artwork and the test point now shows 51 variants, oops (I should give them their own family).
yep I know that, what I meant (but obviously didn’t get across) is that some things such as changing the color bands on resistors are meant to be internal, but if you manipulate the fzp meta data (outside of parts editor which strips the important bits) you can sometimes convince Fritzing to apply the internal magic to your part that isn’t part of core.
Check in the main window when you are using the selection tool you can also set the units to mm (or inches) at the top where you adjust the location and dimensions of an object. Once you have set those can you confirm they are the right dimensions? I get 2.2mm x 1.7mm for each pad and they are [8.2mm] apart which is correct according to the datasheet
While that is true for a single sketch, that will not modify the underlying part (which is what was under discussion here.) To do that you need to edit the svg files which is a lot more complex.