Bit of extra info here, there is an issue with server 2008 (and I've witnessed this on 2003 as well) where you can end up with the ghost NIC problem from removing a NIC from a VM without uninstalling it in windows first, check this out: http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1179
So, even if you did remove the NIC via code, you could hit this issue.
We didn't even consider using code to upgrade our E1000's to vmxnet3's, it was a manual job. 