Basically, all the information that doesn’t overlap with current information would be added. So if a basic grocery store node only has amenity=supermarket and a name, and the reference data I’ve prepared has amenity, name, phone, website, opening_hours, addr:*, brand, and brand:wikidata, then I would merge the phone, website, opening_hours, addr:*, brand, and brand:wikidata values.
Yeah that’s my oversight in the documentation. Presumably all the objects I’m merging data onto will already have a name tag that I would not replace, but in theory, I would merge a basic Whole Foods Market or Trader Joe's value. I have it right in the data 
Again, this might just be academic given that I think every object I add info to will already have a name that I won’t touch, but it’s a good point and I can look into whether this affects brand or brand:wikidata, for example.
I can remove this on Kroger nodes, and take a closer look on this in the future. I agree this is likely of dubious value.
Interesting, and probably a bridge I or the community crosses if and when it happens. This would have to happen whether or not this import goes forward, unless I’m misunderstanding. Might be some work all for nothing, but such is life.