Mix pretzels and sugar together in a bowl; stir in margarine until evenly incorporated. Spoon mixture into a 9-inch pie plate; press into bottom and up sides of plate to form a firm, even crust.
Bake crust in the preheated oven until edges are lightly browned, about 5 minutes. Cool on a wire rack.
Mix sweetened condensed milk, limeade concentrate, tequila, orange liqueur, and green food coloring in a large bowl.
Beat cream in a glass or metal bowl until soft peaks form. Lift your beater or whisk straight up: the whipped cream will form soft mounds rather than a sharp peak. Fold whipped cream into sweetened condensed milk mixture. Spoon filling into cooled crust.
Cover pie with plastic wrap and freeze until firm, about 4 hours. Let stand for 10 minutes before serving; garnish with lime slices.