Is an existing tool, or plugin with editing tools, which would allow a user to edit geometries of existing records, but from already generated geometry on other layers.
Either
A) Insert a geometry (say, from the clipboard) onto an existing record.
Or
B) Update the geometry (lets say from the clipboard again) of an existing record.
So for an example, you have a record on layer A, it has a geometry. You do some geoprocessing and come up with a different geometry on Layer B and would like that to replace the geometry of a record in layer A.
A tool that would be something like
Copy > Paste (Update geometry of selected record)