If a recipe for caramel corn calls for air popped popcorn, could i use microwave popcorn instead?

I don't think it would be bad, but do be sure that your bagged popcorn doesn't have any significant flavorings already included (i.e. butter, kettle corn, etc.) as that would obviously throw things off. Even if it's "light butter," you'll want to see if you can adjust the recipe to account for that.