That IP information is internal to the Guest OS, nothing to do with vSphere.
If you change the type of the vNIC, the guest OS sees this as a new network adapter.
You will have to arrange to apply the old IP settings on the new adapter yourself.
How to do that depends on the type of the Guest OS.
Also note, taking away the old network adapter will disable all network traffic to and from the VM.
With Invoke-VMScript you can still reach the guest OS of the VM, in most cases.