I would like to list some sceneros for you:
1. James Longstreet refuses Lee's order to begin Pickett's charge.
2. Dan Sickles does not advance to his exposed position, instead staying where Meade orders him to.
3. Jeb Stuart arrives before the battle begins, and is able to take part in all of the fighting.
4. Reynolds is not shot by that sniper on the first day.
5. The South is able to capture Little Round Top.
6. General Issac Trimble is not refused permission to take that hill; I forgot what hill that is.
7. George Meade is wounded or killed. Who would take his place?
8. James Longstreet get permission to go around the Union flank on the second day.
I would like to hear from you about these ideas about Gettysburg. It would be fun to get your feedback about what would have happened.
Well #4 is the anwser to #7 and then it Sedgewick, Slocum, Howard, Sickles, Hancock,Sykes.
#8 Longstreet move around the flank walks right into the 6th corps and most of the 5th corps and some union cav. ether he stops are gets chewed up pretty bad. :Old Juan
That is what happened in Peter Tsoura's alternate history of Gettysburg. Have you read that book?