Magento Observer for Api Calls (Shipment Tracking)

I run a Magento 2 Shop (in Development) and i my order management software communicates via api calls with M2. When sending tracking information, the software sends the wrong carrier code ("custom"), it needs to be a specific carrier. Theres no way to manipulate this api call, only possibility is to write an event observer for M2 to manipulate this data on the fly.