How to set a background image before data input

Hi there,

I want to set a background image like in the screenshot, before the visual is created.

How to do this? I guess i will need the pbiviz.json and /assets folder.

I found how to add background-images permanently (even when dataset is used and visual is created) but is there an easier way for this specific issue?

For example you can easily change the visual-icon in the assets folder. Im looking for a similar way but for a "pre-background-image"