In the past, there have been many script changes which cause older scenarios to be broken. For example, the musket's id is now Blunderbuss, but all scenarios using Musket won't work anymore, unless they get updated. Or, the relaunch change breaks every scenario using Rule_Restart or Rule_BaseRespawn.
I propose creating a script file in System.ocg to maintain compatibility with such older scenarios. It would be sad loosing older content because of such changes; for the developer, it isn't so difficult to modify them, but for the player, this is just annoying. Often, scripts to maintain compatibility are not really difficult to write:

static const Rule_Restart = new Dummy {
    Construction = func() {
        GetRelaunchRule()->EnablePlayerRestart(); // Perhaps also setting the relaunch count depending on the game mode
        return RemoveObject();
        }
    }

static const Musket = Blunderbuss;