Well...
As for my part. Hal Jordan would still be able to be a Green Lantern in the scenario I proposed. I just suggested that in combining the two worlds some things would have to logically happen. If the Sub Mariner and Aquaman both exist then there would have to have been a confrontation by now. Charles Xavier would have detected Black Lightning. Wonder Woman would know or know of Hercules.
...and to my thinking, someone else with more willpower would have been chosen. It's not really altering things as much as the Hulk rampaging through the Graysons. In that scenario Dick's revenge feelings are directly tied into The Hulk. That's a hell of a white whale.
In my scenario, the status quo is kept for the most part. Hal can still be a ring slinger. Emerald Dawn still happens. He just doesn't have the connection to Abin Sur. His dad still got killed in a plane. He still grew up with Carol. He's still trained by Sinestro and Kilowog. All that's happening is that I get Abin Sur and the ring first.
Not that big a stretch considering you're merging two universes.