With the new announcement of objective cards being added via the Priority Objectives expansion, it seems there will be some customization to the Battle Card deck. The LtP guide says in setup you simply shuffle the Battle Card deck and draw the top three of each card type (objective, deployment, condition).
I guess this is a question for the OP or FAQ, but at some point they will need to specify if there is a max deck size, a max card limit of a single card, required inclusion cards, etc. Until then (and maybe after), You could conceivably stack a deck for a certain outcome (which I can see as a valid strategy as long as both players have an equal opportunity to contribute cards to the deck).