I have 2 PCB's approximately mirror images of each other, with slight variants. I laid them out on same PCB file, with board outlines for both, with 1 edge in contact. Is there something else I should do to mark that these should be v-scored? Panelising tool doesn't work as I just want to v-score, I don't actually want to panel them.
I know there's an extra suppliment for 2 board designs on 1 pcb, that's no problem. Will order via jlcpcb, double side assembly.
Brand new interactions and interfaces. 
Easy to use and quick to get started. 
When you want to use V-Cuts you should have one single overall board outline and you then add individual V-Cut lines to define the individual boards within that single overall board outline.
V-Cut lines can only be straight and must extend from one outer board edge to the opposite edge. They cannot extend only part way across the board and obviously cannot be curved.
Just add the V-Cut lines in the Board Outline layer. They do not need any extra form of definition.