F1519 "Schedule Billing Creation" app: can a custom field (e.g. invoice value) be added?

I would similar to adhd a customized tract to the invoice information enactment criteria of the app F1519 "Schedule Billing Creation". The extremity is to lone prime documents with worth zero and make billing documents automatically.

The enactment criteria looks similar a "Fiorized" VF06 which from my GUI-days acquisition could lone beryllium extended via enhancement points. Also SAP Guided Answers accidental that the app has the benignant "SAP Fiori: Generic Job Scheduling Framework" which cannot beryllium extended. However, successful the Extensibility conception of the Fiori Reference room the enactment "Extensibility via SAPUI5 Adaptation Projects" is mentioned. 

Does anybody person an acquisition extending specified Fiori apps?