Well, we are not penalising players if they want to try multiple routes at the same time, but when they will start dating one character, other routes won't be available
There are however optional events which are available regardless of the routelock status. MC scenes are sorts of like side stories with stories involving Kei's slice of life outside of route, including stories focused on the main protagonist, events with a main cast and exploring characters like his sister Tomo or faculty. They also adapt to players' playthrough and are aware of their routelock status, offering unique dialogue based on which route you're playing. So yeah, you can play them without being worried about anything. The scene you have listed (MC012) is also a size 3 event