In some cases support team decide to give bonus subscription time to user. For example, when user found some bugs or service was unavailable for user, subscription should be continued for 3 months with no charges.
Is there a way to change subscription renewal date?
I'm not sure Apple allows you to bypass IAP billing with rewards.
There is no way to do this with an autorenewable. It is quite easy with a non-renewable subscription. However, as KNT indicates, if Apple believes you are giving away a subscription for any sort of compensation you will be rejected.
