I heard if u deffer a semester and then do ur AS then it is not considered a resit but then u will be wasting an extra half year as well as payin for an extra semester.
Keep in mind tht resitin the AS and doing A2 exams together is alot to study, it isnt easy at all means so you have to think abt tht aswell.
Talk to ur programme director they usually got the best options to choose from.