What would you do in half time break?

All things considered these guys were in it for the football from the start. Remember the British officers have to convince Colby that it's an opportunity to escape and only co-operates under order. The Marseilles is a bit cheesy but what else would they have started singing? And I think the fact that they actually managed to get a draw against the German national team from 4-1 down shows they were right to believe they could win. Seriously them escaping at half time is a good ending? Think about it, it would be a simple end to the film, where's the excitement? And while the Nazis may have been ruthless publicly machine gunning down an entire stadium of civilians to keep tabs on 20 POW's would not have happened.

At half time I'd probably have changed to 3 at the back and strung 5 across midfield, thus cutting the german's supply route to goal.

I'd run most likely, but you have to consider what this movie is based. It's based on a series of games between some Ukrainians and Germans, and the Germans said if the Ukies win they'd execute them, if they lost they'd let them live. And yes, the Ukrainians won. So some people in those situations would do crazy things, as movie cliched as it seems.

How would this movie have been if Polanski or Zeffirelli directed it instead? More successful, LESS successful? Different actors?

Say Arnold Schwarzenegger instead of Stallone? (Actually probably would've made more sense since Arnold's German but he would've played for the Axis team, not the Allies).

Actually, Stallone could've been Italian since that is his real-life ethnic heritage. But again, that would mean he would've been on the Axis team.

Die of exhaustion. I get sore just WATCHING the players run!

Would I have escaped? I don't know. Paris was still occupied by Nazis so you definitely would've run into a Nazi-goon eventually unless you went to hiding. The borders would've been closed so trying to get to Switzerland or America would've been out of the question. And I think this was 1942 so you're looking at 3-4 years before V-E Day. Still would've be better than getting recaptured or worse.

And still unless you're Jewish (no disrespect here), you're probably safer dealing with Germans than Japanese in any scenario.