On Jackie Robinson Day at Rangers Ballpark and all of the players wear number 42, I don't read everyone's number as number 42....when doing the lineups, I announce their regular number. We make an announcement prior to the game for the reasons why all players are wearing number 42.
We also can't change all of the numbers on the scoreboard to 42 either. The scoring system works off of rosters provided by MLB and the statistics operate off of a player's number....such as TEX32, that then tells the scoring software to update all of Josh Hamilton's stats for that day, his number on the scoreboard, where he is from, etc.
But we don't announce every player as wearing number 42....we announce their regular number during lineups.