Hello Bill,
The functionality that you are asking for is something that has not yet been implemented in EA.
I believe the easiest way for you to acheive your goal, is to export your entire model to XMI, (in the browser, right-click on the model root node(s) and select "Export model to XMI"), then create a new, empty model and Import from XMI. That will create a copy of your model, without any version control.
Then, in the new model, define your VC configuration and apply version control.
EA version 7.1, released yesterday, now has a command "Add Branch to Version Control". This should make the process somewhat less tedious.
If your model is stored in a third-party DBMS, you probably should re-create it as an EAP file, as an intermediate step. Once you are satisfied that the EAP file is complete and version controlled as you desire, then use the Data Transfer facility to overwrite the old model in the DBMS.
p.s. I am curious to know which VC product you are changing to...
regards,
Howard Britten.