Could one solution to that issue, be to actually have the savegame-file being stored in the subfolder of the selected level itself? The load game menu both inside the main meny and in-game would have to include the ability to browse subfolders inside the main folder itself then I suppose, like a subfolder-browser on the very top inside the load game menu.

Then all the savegames inside the selected subfolder would show. Also, saving in a folder other than the one that contains the level itself would not be allowed by only having the savegames for the folder of the selected level shown when saving a game, without the option to browse folders in general while inside a level.

If it's not possible to have such differences in both the save- and load game menu (hence a hypothetical subfolder browser on the top being shown on both menus), just disable to ability to browse folders inside the save game menu.

This is only some thoughts I had just now. I have no idea what's possible to do with all the current techniques and partial source code the Jazz2+ team have for modifying the game as of today.