Add pudding, root beer, evaporated milk, and root beer concentrate to a mixing bowl and whisk for 2 minutes until smooth. Refrigerate for 5-10 minutes to allow to firm a bit.
Reserve 1/2 cup of whipped topping and set aside in the refrigerator.
Fold remaining whipped topping into the pudding mixture and spread into the graham cracker crust. Cover and freeze overnight.
When ready to serve, remove pie from the freezer and top with reserved whipped topping and cherries. If desired, put whipped topping into a pastry bag fitted with a star tip and pipe onto the pie. Top with cherries and serve.