Exactly that. Each instances has it’s own rules and as such, you can make your own on your own instance. Just don’t be surprised that some instances block you for not abliging to their standards, as they also control their own federation, like each individual instances.
You can. It just show you everything that need additional info. You can just choose to move the map to the shop you want to edit hours and do that. You can also filter the StreetComplete missions in the settings if you want to only update business hours and description.