Is it one tilemap object or four different ones?
If four different, you will have to make templates with the same name for every tilemap object. For example "boss_room" template for TilemapGrass, TilemapFire, FilemapWater, TilemapPoison. Then you can spawn a tilemap object by name.
If it's a single tilemap with 4 tilesets in it, maybe you can place these tilesets at regular intervals (say every 50 tiles). Then after adding a room, loop through all tiles and update them.
For example, if it's tile number 23 and you want it to be from the second tileset, you change it to 23+50.