How to add a scenario to an existing game (Memoir '44)

[MacGreenbear]

I've read through the documentation, which is great if you are creating a game. What I couldn't find is information on how to add to an existing game. I would like to add a scenario to Memoir '44 but can't see how to get at the existing code.

Am I overlooking something? Please advise..

[ufm]

Custom scenario option is already there as a premium option