Are you wanting a smaller board size? Just reduce the number of Spots in the PlayArea, and move them where you want the tiles to be spawned at. You could just move them to a different object or something as well.
It is a little more challenging to maintain an equal number and I'd have to look at it for a while to cook something up, likely the spawning system will have to be changed quite a bit. The computer needs to know how many of each tile to spawn, so that would be the available spawn points divided by the number of tile options.
Then it needs to know where to spawn them, if its in sequence then you can use Get Next Child to store the spawn point, if its random then you need Get Random Child and also have to destroy the Spot you just spawned into so that it doesn't randomly choose it twice on accident.
It also needs to know how many of each tile that it has created, so you can likely use the existing subtraction method, but have a separate integer for each tile type you are spawning.
You can do it though, its just a matter of thinking through it and experimenting =) Figure out what the computer needs to know and find a way to give it that information.