The Alter Choice block allows you to alter the way choices are displayed according to different variations. It should be connected to the choice point corresponding to the proposal whose appearance you wish to modify (delete, cross out the choice or replace it with an image) in the Choice block.
Some options imply the use of boolean variables to be effective. This is the case when you want to suppress an already chosen proposition. In this example, the player does not have "Rue Verte" as an option because he already went through.