we just published our 1st web map using AGO WAB interface. Now we are looking to add more layers to the map but don't want to interrupt the use of the app. How can we do that?
It's not possible to edit/modify a Web AppBuilder app in ArcGIS Online without interrupting its use. I suggest you make a copy of it, then apply changes to the copy.
Hope this helps,
Seem you want to add more layer to the web map first without interrupting the web app, therefore, I had recommend you do a "save as" for the web map (see image) as well as the web app ( as suggested by Derek) then do a switch after you have tested the outcome.