Hello
Welcome to OSM.

We don't use post partner in the UK, post offices within small shops are considered post offices, you can do most of what you can in a larger post office so they really should be amenity=post_office.

They are standalone counters within the shop, usually with their own opening hours. It is more usual to map them as a node within the larger shop mapped as a way.

What triggered you to change this and others?

Cheers Phil