We should not fear these shopkeepers. If any shop has the temerity to ask if you are exempt when you enter unmasked, tell them very firmly, "No." Make sure you video what happens. Better still, go with someone who can video the event. If the shop tells you to leave or they will call the cops, then walk out. I expect they are within their rights to bar entry to anyone they choose (but I am no lawyer so I could be wrong here). Shame the ******** on social media. Broadcast their name to all and sundry.
Stand up for your rights. If you don't know what they are, read this: