That's sad to hear. I guess we will have to leave the pre-determined vAppNet- name.
Yes I can confirm that setting a civm to no network, then to a new one, it loses it's internal ip in a routed network.
get-civapp "Test vApp" | get-civm | Get-CINetworkAdapter | Set-CINetworkAdapter -vAppNetwork $null
or using the extensiondata property of the civm and setting the network to none/$null clears the IP it had.
Even if it didn't remove the IP, the amount of required to that for each VM is not worth the gain.