Sometimes it would be useful to be able to make arbitrary modifications to the JSON that gets pushed to Apple or Google from the UI. Right now you can add things like "content-available":1 to the JSON if you push via API, but there's no way to do the equivalent if you create the push from the UI.

Ideally there would be some sort of JSON rewriter that would start with the JSON sent by the UI, then allow the developer to modify the output of that before the payload gets sent to Apple/Google with various rules (add JSON, pull out values, substitute body inside something else).

This would allow customers to have full control over what gets sent to the push provider if they want/need it, and also make things more robust if push providers change what is required (the default rules could be stored in a database and changed by WCA).

Note that each notification might potentially need different rules - I might want to add a "launch-image" to one of my messages but not to all of them.