I've headed off to bed.
Bad news - I'm not going to be able to add slots to the 2x2 table, and all 2x2 tables have the same layout. Apparently, adding slots stuffs up the animation.
Good news. I'm going to make a 2x2 omsp, that you can use to slot things onto the table as you like.
I've done a bit of investigating.
This thread at MTS2 is the one that is the interesting one I think - http://www.modthesims.info/showthread.php?t=445472
The terraintype cheat is not completely working when it comes to existing hoods.
According to Mootilda its fixable:
"Did you follow the instructions for resetting the lot terrain? ie, pick up the lot and place it down again in the neighborhood view. This step should reset the lot terrain to match the hood terrain.
The terrain type is stored in three different places. All three must be changed.
1) The main hood terrain is stored in the neighborhood terrain geometry (NHTG) record. This is the terrain which is modified using the TerrainType cheat.
2) The terrain underneath the road is stored in the neighborhood memories (NGBH) record. This is the terrain which you change by extracting that record, modifying it, and importing it again. Why EA didn't change this with the TerrainType cheat is beyond me. Why they stuck the terrain type in the memories record is even more mind-boggling.
3) The lot terrain is stored in each lot description (LTXT). You can reset the lot terrain by picking up each lot in turn in the neighborhood view, then placing it down again. "
I may be on later, but I'm going to nap now.