I spend a lot of time managing AGOL webmaps for use in Collector for ArcGIS. I have to make changes to various existing web maps on a daily basis. The only way to manage these web maps seems to go on AGOL via web browser. Our internet can be unreliable at times and just adds to the poor inefficiencies I have to deal with when changing a web map, either by adding a new layer even changing symbology.
I have noticed there is way to override an existing web layer, but not a web map.
Am I missing something here?
I think you're looking for https://community.esri.com/ideas/11949, correct?
I'd encourage you to visit that idea, up vote it and add your use case to the comments.