We are beginning the process of migrating our colo to another site, a different physical location. In our current site we have a vcenter 6.5 cluster setup with 5 host and lots of VMs. The new cluster was installed without installing enhanced link mode, esxi ver is 6.7. It is my understanding that the way to migrate between clusters is using enhanced link mode and enhanced link mode needs to be installed before ESXi. is this true? can we install enhanced link mode after the fact? If we cannot how can we migrate VMs between 2 independent clusters other that explorer\copy\paste?
No, Enhanced link mode doesnt need to be configured before you have setup ESXi. You will need an enterprise plus licence though, i assume you have this? Here are a couple links you may find useful including one on cross vcenter migration
Joining a vCenter Enhanced Linked Mode Domain
Cross vCenter Migration:
I second the idea of using the free tool called Cross vCenter Workload Migration Utility. Another option is to purchase HCX.