Hi, @PFarkas👋 I can confirm this isn't a feature. The options for Notification settings are all set in-app — Set up User Notifications. There isn't an option to alter this behaviour when creating Deals via the API.
If you have a moment, adding your suggestion to the Ideas Community and getting some upvotes will be very helpful in getting your suggestion in front of the Product team. If you add a link back to your Idea post, I'll be sure to give it an upvote to help get the ball rolling.