Adding forest root domain after-the-fact

We want to migrate two domains with poorly designed namespaces into a new domain with the proper namespace. We’re not sure, however, if this is possible since we would be effectively adding a parent domain as a root to an existing child. Here is the current situation (with names changed to protect the innocent):

Old domains:
root.xyzcorp.business.com
xyzcorp.local

New desired domain:
xyzcorp.business.com

As we would like to do this in stages, can a new forest root domain (which would be the parent of the subdomain “root.xyzcorp.business.com”) be added? If so, how would this best be approached?