If I want to change an A record, which is being referenced by several CNAME records... I'd ideally like to just click a "Migrate to new A record" button... which would either let me pick an existing A record, or enter the name of a new A record... and then update all CNAMEs (within the zone) to use the target record.
This feels like a very specialized scenario. I don’t think we can justify supporting this in the Azure Portal.
Please note that it should be possible for you to implement this in a script, building on the Azure PowerShell cmdlets or cross-platform Azure CLI.