score:8
I do this regularly for plane spotting. Border guards at ZRH do not require you to show a boarding pass. I just show my (Swedish) ID card and sometimes they ask where I'm going, in which case I just make up a random city where there's an upcoming flight. Done!
And yes, you can go back with no issues - just follow the signs for the A/B gates.
Upvote:4
I visited the concourse E without any trouble. When the agent at passport control asked me where I was going, I simply told him that I'm visiting a specific lounge on the other side, and he let me through.
When I came back I had to go through customs and I had to pass one more time through security.
I also managed to do this on Frankfurt. I used the new, automatic machines that scan your passport and take a picture of you, in order to let your through (I didn't need to explain myself to an agent)