Yes, the level editor can see it, but the real way it reads it is via a 12 bit array. You see, the variable for a tile, defined in any tiles[] call, is really a hex value along the method of 0xABC.
A = A 16 peice division of the current tileset, along these lines:
For B & C:
B=The vertical plane.
C=The horizontal plane.
Also, all prefixed zeros may be trunicated. So, using this principle, the first plain grass tile would be located on the first section, in the last column, and on the last row, giving the value of 0x1ff.
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So, your appendage of extra tiles onto the level array simply would not work, because it exceeds the range of the variable.