Push data via API into an existing model

Without the ability to define my model in Excel or the Power BI designer with relationships and DAX calculations and column properties/formatting, it's going to be very difficult to get my dashboards to work and look as I want. I would like to be able to upload an Excel or Power BI Designer model then use the API to push new data into it real-time. I'd also like to be able to schedule refresh and decide what happens to the API pushed data during scheduled refresh. For example, I may upload a model with 100,000 rows, then use the API to add 5,000 new rows. But during scheduled refresh those 5,000 new rows are also in my SQL source so I want to wipe out the API pushed data upon scheduled refresh.