Moderator: Moved to vSphere Upgrade & Install
Changing the domain from x.local to y.com would be changing the FQDN of your vCenter Server host name. Example: vcenter.x.local to vcenter.y.com
1. Take a backup and snaphot of the vCenter Server.
2. Take a backup of vCenter Database.
3. Follow the below KB article to change the vCenter Server hostname to the new domain name.
https://kb.vmware.com/s/article/2146301- Please follow the steps mentioned in this KB article to change the hostname of vCenter Server. You need to change the hostname of vCenter and stop all vCenter Services mentioned below, then delete the certificates mentioned in the KB article and then uninstall the vCenter Server, reboot the vCenter server and reinstall the vCenter Server with the same version of the vCenter Server.
To stop all the 5.5 vCenter Server
VMware Certificate Service
VMware Directory Service
VMware Identity Management Service
VMware Kdc Service
VMware Single Sign-On STS Service
VMware vCenter Inventory Service
VMware VirtualCenter Management Webservices
VMware VirtualCenter Server
VMware vSphere Profile-Driven Storage Service
VMware vSphere Web Client Service
VMware Log Browser
vSphere Install-Upgrade Support
is your old vcenter 5.5 based on windows and you plan to migrate to the appliance ? then switch over to the new domain before is unnecessary. just migrate vcenter to the appliance and then join the appliance to the domain.