I'm a little surprised someone hasn't looked at the APA Rule Book. In the Team Manual under Rule 11, it states that, "Once both teams have declared a player, the players cannot be changed unless a team's choice of player will cause the team to violate the Team Skill Level Limit rule or the Limited Senior Skill Level Limit rule." It appears that, under the rule, the choices cannot be changed once BOTH teams have declared a player. The implication is that until the second team has selected a player to complete the matchup, the first team selecting is free to change it's mind. This makes sense. If the first team selecting changes it's mind, so long as the second team has not made a corresponding selection, there is no competitive advantage in the first team changing it's mind. The second team still gets to react however it wishes.