I thought I heard in a technical session at the Partner Conference that it’s possible to “reuse” an existing map ID for a newly created layer. I know this sounds odd, but I created some layers for a project and I have recreated and republished those layers. They, of course, have a new map id now. I have several instances that are pointing to those original map ids. It would be great if I could delete the original layers but use their map ids with the newly created layers. This would be a huge help for the ongoing development work I am doing on this somewhat large project.
Have you tried doing this in the Assistant? I haven't tested this but I would think it might work and I'd be interested to hear if it does for you. Delete the old webmap, and change the new webmap item ID to the what the old one was. I imagine if schemas (if there is stuff specific to field names; that may or may not be the case, may not even matter) apps pointing to the old webmap would work.