Webhook Event for pending subscription changes

Webhook Event for pending subscription changes

Hi there!
I am updating a subscription by using the API. I am making changes (increasing addon quantity) with end_of_term = false. I want to setup a Webhook to catch this event but I can not find any predefined event for this case. Also I can not find a way to catch this event by defining a custom event due to the limited options. Is there any way to trigger a webhook when a subscription has pending changes that will become effective in the next billing cycle?

Appreciate your help.

Sincerely, 
M. Muehlstaedt