***This idea is logged on behalf of a customer***
Create a new layer using an existing web service with desktop tools like ArcGIS Pro or ArcMap.
Desktop tools have the ability to create very detailed layers but when you publish layers from the desktop tools you create a web service and a web layer.
From here you can open the web layer and make changes and save a new web layer, but you do not have all of the tools available in ArcGIS Desktop.
Have the ability to use a layer created from ArcGIS Pro or ArcMap which contains a web service to a new layer that uses an existing web service could be really helpful.
A workaround might be to publish a new layer with a web service and then use AGO Assistant http://ago-assistant.esri.com/ to modify the layer to use a previously create service. Later deleting the extra web service.