That's fine.
But I was playing around with it. Problem I'm facing now is that gamesaves (including autosaves) are "multiplayer". To enable a mod you have to select "single player" first. But then you don't have access to multiplayer gamesaves folder. But even if you move the gamesave, it won't open.
And the game menu and options screens think you are in muliplayer, so act differently.
This might require a more complicated hack to really work.
Edit:
Playing around with it some more:
PreGame.SetMultiplayerGame(false) doesn't work. PreGame.IsMultiplayerGame() still reports true. However, you can go in and out of multiplayer with:
PreGame.SetGameType(GameTypes.GAME_NETWORK_MULTIPLAYER)
PreGame.SetGameType(GameTypes.GAME_SINGLE_PLAYER)
Using GAME_HOTSEAT_MULTIPLAYER above doesn't remove the leaderscreen.
Once back in single player, you can save a game and load it.
So, maybe solution is to set multiplayer only when leaderscreen would appear. Or, conversely, set single player before gamesaves occur (or when before player goes to game menu). Unfortunately, both of those are complicated.