Yes! You can edit while the game is running as the Diamond app allows coaches to add new players to a lineup or add a new pitch/play in seconds.
To edit a lineup, play, or pitch during a game:
1. With the game active, click the + icon in the top right corner
2. Make any changes needed to the lineup, plays or pitches.
3. Click save and the new info should be added to your list in seconds.
(Note: You CANNOT add new games to your list while you have a game running.)