Short answers, pulled from the story.
The Cleveland Browns, San Francisco 49ers, and Baltimore Colts joined the National Football League intact on the 9th of December 1949. These franchises were part of a merger that brought the total number of teams to thirteen for the 1950 season.
The league established the Pro Bowl as an annual event starting in 1950. Previous attempts at all-star games between 1938 and 1942 were cancelled due to World War II and never revived until this new format matched two division-based all-star teams against each other.
The free substitution rule returned permanently during the 1950 season allowing any player to be replaced after any play. This change paved the way for specialized units within each team including offense, defense, and special teams.
An exhibition match took place outside the United States for the first time when the New York Giants played the Ottawa Rough Riders on August 12. The game occurred in Canada under the Interprovincial Rugby Football Union banner.
Ties at the end of the regular season forced an unprecedented four-team playoff system involving the Browns, Giants, Bears, and Rams. Both divisions ended with multiple teams sharing first place records requiring extra week tiebreakers before the NFL title game.