Auto process orders only for subscription renewals

Hello,

My setup:
I use WooCommerce to sell API keys as a time-based subscriptions.

I added the subscription add-on and software add-on to the store.

What I want to do:
Subscription renewals are creating a new order and this order has the status “processing”. I would like to auto process these orders directly to “completed”, because these are known customers.

New subscriptions on the other hand should still get manually processed and checked.

I tried some auto-complete plugins but they all can not distinguish between a new subscription and the renewals.

Any ideas for working plugins or which files need some coding?

Thanks in advance!
Jan