Is there a way to import users without overwrite the metadata?

Im looking for a way to solve the problem of data being overwritten when doing a user import job.
Currently I have 2 tenants, dev and prod. I maintain the same users on both tenants, exporting users from dev to prod periodically, so the flag UPSERT in the user import job is always TRUE, as I don’t want auth0 to create new users but update the existing ones. However, when I modify the app_metadata object in dev tenant, and do the import job, the object in prod tenant is being replaced by the object coming from dev tenant. The process of exporting or importing users requires a JSON file with a structure used by auth0 as the user data, even when I only pass the new fields in that JSON file as app_metadata values, the app_metadata in prod is being totally overwritten. I don’t want the app_metadata to be replaced, I just want the object to be merged as it does with the update user API endoint for example. I search first for an option in auth0 to do a bulk user update without success. I don’t know if there’s another option to solve this problem.
Any help would be appreciated.