I don't have a clear understanding but I do have a couple of rules to go by.
1. It is a labeled as a restaurant according to their business license.
2. If they use a majority of their business hours to serve food.
When you say "turns into a bar" what exactly makes it turn to a bar? Do they begin serving more alcohol than food at night?
If so, I wouldn't use that as a reason to assume it's a bar by law, but instead just more people congregating and drinking while watching a sporting event. If their commerce is still mostly food throughout the day, then I'd say it's safe.
I'm not a lawyer, and I'll argue my side that I'm perfectly legal if a cop ever sees me carrying while at a restaurant that is serving a lot of alcohol to people because it's night time and football/basketball/baseball games are airing.