Hi Amanda,
I was experimenting with this recently and my (admittedly quick) initial findings were that you can use the ArcGIS Online Assistant to update ItemIDs and feature service URL references in app widgets. But you need to make sure you properly catch every instance of the URLs/ItemIDs. I was able to get this quick test to work:
- Update the web map using the I Want to --> Update the URL of services in the map (as you know, this updates the map but then breaks the widgets).
- Update all of the layer references in the I Want To --> View an Items JSON --> click App --> manually Update all URL references and/or ItemID references in the JSON in both the Description and Data areas.
I used Brackets to work with the code, and made sure I backed up the original JSON. In my apps I found that I had to update full URLs for the widgets, not ItemIDs. That is likely the result of the way I added the services to my web map originally - I directly pasted ArcGIS Server URLs rather than add registered services.
Doing these steps (carefully) resulted in a web app with widgets and map layers that were changed from one map service to another. The caveat is, of course, that the feature class data structure should be identical (i.e. same attribute columns). If it isn't, then you might need to dig further into the JSON code. Also, I only tested relatively simple widgets (Search), I don't know how crazy it gets with ones like Infographics.
As with all of this, it would be best to try it in a test version before working on production data. Heed Esri's warning that "this is untested and unsupported"...
