Deleting a game from the Book
How do I delete individual games from an opening book?
An opening book is generated from games which have been imported. For many moves the only information stored in the tree format refers to the number of games in which this move occurred.
For example 1.e4. For this move the tree stores the information about the number of games and the statistical probability of a win based in the games imported. For that reason it is not possible to delete individual games from the tree of positions.
You can delete individual moves from the positional tree, but not specific games.