Actually, from everything I've seen, the movie didn't change at all. They didn't "retool and reshoot" anything, just converted to 3D and keep it out of the backwash of Avengers. With that, the delay was only nine months, and paramount likely didn't spend extra on marketing when they really didn't have much going before the first release date
At minimum, they shot more scenes with Channing Tatum and Dwayne Johnson, because they realized they were killing off a newly minted Hollywood star in Tatum and wanted to milk him for all he was worth on the way out the door.
I think the new scene was the one of Duke and Roadblock gaming at home, because test audiences apparently liked the chemistry between Tatum and Johnson.
I mean if Tatum's star was that precious they would've rewritten him to be in a coma instead.
Duke not being dead would have been a stretch, even for that stupid ass movie. "Let's avenge Duke" is one of the major plot points. Plus I imagine Channing Tatum was more than happy to move on.