One-time discount on an existing subscription without resetting the price

As a coach, I want to be able to apply a discount to an ongoing subscription for only the next payment period, without permanently changing the fixed subscription price. After that period, the standard rate should automatically apply again. On the invoice, I want to see the original amount and the one-time discount with a clear description. This way, I do not have to temporarily lower the price and manually adjust it after the direct debit.