Recommendations on unmount parititons of active VM in order to change UUIDs?

I'm trying to speed up our deployment of RHEL VMs, as we use vCenter. So I've created a VM, converted it to a template and then spin clones off of that.

Of course we have to change the UUIDs for any of the partitions that fall under LVN.

My question is how do I unmount these partitions while the VM is up and running in order to change the UUIDs? I always seem to run into something running that won't allow me to unmount.

IMO, it almost easier to create a new VM from scratch Vs trying to umount partitions and update UUIDs.