Stir 4 cups milk, white sugar, and rice together in a slow cooker until the sugar dissolves; add margarine.
Cook on High for 2 1/2 hours.
Beat egg, 2 tablespoons milk, vanilla extract, almond extract, and salt together in a bowl.
Temper the egg by stirring a small amount of the hot rice mixture into the egg mixture to gently warm the egg without cooking it; stir the egg mixture into the rice in the slow cooker.
Continue cooking on High until creamy, about 15 minute more.
Transfer pudding to a glass baking dish, cover with plastic wrap leaving two corners uncovered to vent, and refrigerate until chilled completely, at least 1 hour.
