Virtually all items in Portal (and ArcGIS Online, for that matter) have some sort of JSON representation associated with them, even if it is just a description (think metadata). Many items, including Web Maps and hosted Web Mapping Applications, also have data associated with them, and that data, to a certain extent, can be manipulated from right within the AGO Assistant. Yes, you can edit an item's JSON, save the changes, and they are immediately live. To view an item's JSON, log in as the item's owner and under I want to..., select View an Item's JSON:
Click on a folder in the left panel to expand it. Any items with ...
