Once you have made network changes (802.1Q) and you have lost (oops) connectivity to your service console, use the following to change the VLAN tag:

esxcfg-vswitch vSwitch0 -v N -p Service Console

Where N is the VLAN tag you want to use. In this case it was vSwitch with the portgroup name Service Console. To list the current configuration use:

esxcfg-vswitch -l