The mechanism is explained in this article:
Changing or keeping a UUID for a moved virtual machine
In you case you should go with "I moved it" it. Otherwise, when you select the copy option, it will generate a new UUID and a new MAC address for the vNIC as well, which in most cases causes the GuestOS to lose static IP information.
By the way, you don't need to incorporate downtime for your VMs for this migration if you already have shared storage and network access. You can just disconnect hosts from the old vCenter and add them to the new one, and then vMotion the VMs to the new hosts.
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