As CarolMN notes, there is usually no problem re-entering the World Showcase prior to its 11 am opening to return to your resort. Sometimes the CM standing by the rope asks for a room key, sometimes not, but I have never been prevented from re-entering. You can only go past Canada and England and then over the bridge to the International Gateway. There is another castmember at the rope blocking access to the bridge over the canal on the way to France.
In a similar vein, when you arrive at the other World Showcase entrance near Mexico on your way to Norway for the breakfast, you will have to tell the CM at that rope that you have PS for breakfast. They do not let you wander around the WS prior to opening at 11 am, but you can pass through on your way to Future World (to start your day with a ride on Test Track or with Figment, for example) or to return to your resort after your excursion.
I don't know if they try to control the direction departing guests take when leaving the Princess Breakfast. It may then be possible to at least walk through the World Showcase in the direction toward China, Germany, etc. rather than going back toward Mexico as you exit the park.
A few years ago, I took a half-day photography course offered by the Disney Institute. We had an initial training session at the institute and then arrived at the back entrance to Epcot about 9:30 am. We had 90 minutes to photograph whatever we wanted to in the World Showcase prior to opening. There's some really interesting architectural and decorative elements that you only really see up close in the absence of the usual visitor traffic. We were warned that if we left the WS for Future World, we could not return until 11 am. I reserved my picture-taking in FW for after 10:30 so I could then return for the return trip to the institute about 11:30 without difficulty.
Ralph