How to update game with new levels but keep new levels separate from the main project?

I'd like my game project to exist online and get updated every few days or so with a new level. Levels aren't continuous - you pick one to play from a menu, you finish it, if you want to keep playing, you pick another level. A level is contained in its own layout within the project.

I don't want to keep adding the new levels/layouts directly to the project and wind up with one giant download just to play a single level. The levels reuse sprites, scripts, event sheets, etc. from the main project, but also have a unique image just for that level. It would be nice to be able to save a layout in a file separate from the project and load that as a level as needed.

Any thoughts on how to structure something like this?

Since you're already using a server, you could have a stock of Jsons that are essentially the states for each level. The user would then request the level's Json on load and in turn the game creates the scene accordingly.

Hope it helps.