New api to sync nova.instance_extra with its changed data in nova_api.flavor_extra_specs

I am seeing some issues, and believing there is something which can be changed...

When a VM is created for a reason which I don't know why, its flavors extra properties are completely copied to a row on nova.instance_extra, and from then on if you change original flavor nothing will be changed on the flavor of the VM. this is natural on openstack and there is now flaws, I think this is slightly will cause speed up in the query instead of aggregating all the flavor properties from the database again.

But there are scenarios which will force us to change this data, for example to migrate from network qos set on flavor to new neutron qos api, we are forced to do it directly on its nova.instance_extra record, as long a VM is running it is using the old quota, and as it is rebooted it will let go of the old quota properties.

I was thinking can there be a new API for admin to call and it actually syncs the VM flavor with its changed data?
I am also a developer and can contribute on this if it is needed.