Q. I cannot change the VLAN number of a site in a Logical Network in SCVMM, why?

A. You cannot change the VLAN while a site has an IP pool created (which cannot have allocated IP addresses). Once the pool is deleted you can change the VLAN ID. It's important the VLAN ID is correct or traffic will not traverse the physical network. If your network is set to untagged then no VLAN should be specified and the VLAN ID should be set to 0. Only if the network is set to tagged and expects the traffic to be tagged with a VLAN ID should you set the site.