You can trigger tile creation.
-1 means that the tile is randomized.
- Environment - Change terrain type at (Center of (Playable map area)) to Barrens - Pebbles using variation -1 in an area of size 52 and shape Square
This way does not break the limit of 16 tiles.
I recommend JNGPE for that, although both ways work.
But the 16 tile limit is already with JNGPE.
There's a third way to get around tileset limit. Normal WC3 editor has it's own limit, JNGPE lets you use up to...I think 100 tiles? Not sure.
But, you could also modify your Terrain.slk in War3patch.mpq and remove the texture space that each tileset takes. (I think that would work, anyway. Not tested this.)
The actual amount of tiles used doesn't really seem to effect much in-game, as JNGPE can demonstrate. So theoretically, doing this, you should be able to use literally every single tile in one map.
Even if it works, you'd need a custom executable for this method.
There's a third way to get around tileset limit. Normal WC3 editor has it's own limit, JNGPE lets you use up to...I think 100 tiles? Not sure.
100 tiles?!?! Is this true? I've never been able to select more than 16 at maximum. Is it possible to get more than 16?