This problem has come up a couple times and I figured out how to do it. It isn't a pretty thing to do, but it works.

First, open your terminal and go to /Library/Application\ Support/VMware\ Fusion/

sudo ./vmnet-apps.sh --stop

If you want a host only net, cp -R the vmnet1 folder, if you want a NAT network cp -R the vmnet8 folder. Name the new folder vmnetX where X is your new network name.

Edit the files inside. There is a dhcpd.conf which must be changed to suit your needs, if it is a nat network there is a nat.conf and a nat.mac. Change these to match the dhcpd.conf changes in networks.

Now edit the networking file. If you want a host only network, copy the VNET1 entries, if you want NAT copy the VNET8 entries. Paste and modify the entries to match your vmnet folder's #.

Now delete the VNET_X_DHCP_CFG_HASH line, it will auto-regenerate.

Edit the lines to match the network etc. If you want the Mac to NOT have a connection (aka a self contained vm network) set VNET_X_VIRTUAL_ADAPTER to no

Now run sudo ./vmnet-apps.sh --start

Do an ifconfig and make sure your new vmnet is up and correctly configured.

Now go into ~/Documents/Virtual\ Machines.localized/

cd into your VM you want to mess with (note ADD THE ADAPTERS IN THE UI FIRST)

Modify the .vmx of the guest

From source:

For a VM with VMware tools installed:

ethernet0.present= "true"
ethernet0.startConnected = "true"
ethernet0.virtualDev = "vmxnet"
ethernet0.connectionType = "custom"
ethernet0.vnet = "vmnetX"

For a VM without VMware tools:

ethernet0.present= "true"
ethernet0.startConnected = "true"
ethernet0.virtualDev = "e1000"
ethernet0.connectionType = "custom"
ethernet0.vnet = "vmnetX"