Keep CUCM,IMP,CUC and expressway C on XYZ.corp
Keep expressway E on XYZ.com. make a subdomain on internal DNS and add an entry for expe.xyz.com to your internal NIC IP.
Make required changes on public DNS.
If you change domain this will also regenerate the self signed certificates, if using CA signed for internal servers you must sign it again.
Btw if you are using two expressway C which is a cluster and one expressway E this is not a right design. you must have same number of nodes for both E and C when making cluster..