Yes, but you would probably never see it done since then the play would be about ten yards (where the ball would be held for the PAT try) instead of two yards. Yes.
No, at that point in the game they are automatic booth reviews.
If a NFL Coach wins the challenged play, he still loses one of his two challenges. If both challenges succeed, then the team is awarded a third challenge.
After a touchdown
You can't ... all challenges in the final two minutes of each half (in the NFL) are initiated by the replay judges. If the replay judges determines that the play should be reviewed they will notify the referee.
No. All other levels leading up to the NFL you can though.
The NFL began allowing 2-point-conversion attempts in 1994.
No. The two-point conversion play was disallowed when the AFL merged into the NFL and was not resurrected until 1994.
In the NFL, after a touchdown, a team can choose to kick an extra point or go for a two-point conversion. An extra point is worth 1 point and is kicked from the 15-yard line, while a two-point conversion is worth 2 points and is attempted from the 2-yard line. The outcome of these point after attempts can impact the final score of the game by adding to or subtracting from a team's total points.
In the NFL, if a team blocks an extra point attempt, they can return it for a touchdown and score two points. The opposing team cannot score any points on a blocked extra point attempt.
Each team gets 2 challenges to start the game. If the team uses both challenges and is successful with both, they get a third challenge. If the team uses both challenges and is not successful with both, they do not get a third challenge. Three is the most challenges a team can have in an NFL game.
Cleveland Browns against the Cincinnati Bengals on September 4, 1994. The Browns actually faked a PAT kick and holder Tom Tupa ran into the end zone for the first NFL two point conversion.
I am not sure of the exact game but it was during the 1999 season. Here is a link to a good description of instant replay over the years. http://en.wikipedia.org/wiki/Instant_replay -----The answer above describes instant replay in the context of helping game officials make the correct call. The first time instant replay was used in an NFL broadcast was during a preseason game between the 49ers and Colts on August 6, 1965.