Multiple VLAN's available to VM's - networking questions

I need to add some more VLAN's for my VM's to access, so I have added another logical network with a network site that contains all of the VLAN's and IP subnets that I'm going to need.  To be able to assign a different VLAN to a VM, I think I will need to change the settings in the Uplink Port Profile so that it will support the new network site.  If I check the box and hit OK to add the new site to the UPP, what is going to happen?  Will it be seamless or will there be a short outage (or worse yet, a total failure!).

The UPP that I need to modify is used by almost every VM I have, so I'm a bit hesitant to try this unless I know what's going to happen.

Another question -  is there some way to create a singe VM network that would support all of my VLAN's/subnets?  I have tried going into one of the current VM networks and adding another VLAN, but there is no Add button.  I assume maybe that's because once it's already assigned to resources they can't be changed?

Ideally, I would like to have just one VM network and when I go to assign that to a VM, then I could just choose the VLAN I want, instead of having to create VM networks for each VLAN.  

KW