they're called 'transition tiles'. These also include those you mentioned of the 'sea-land interface' , along with those between the various terrain types (desert to farm, farm to mountain, mountain to desert, city to whatever -- usually all others)
For example, say the region of the Qattara Depression, you create a "gravel field' tile for the center. Then you need to make 3 transitions -- gravel to desert 25, 50, and 75%. So, each single tile is actually a set of 4 tiles. This does not include any 3-way tiles (like gravel to desert to mountain, for example - of which 2 are needed, mirroring each other ie: gravel to mountain to desert)
TOD importation is something very few have learned (I'm not one of them!). I know it CAN be done There's provisions in the TE for 'adding new 3d objects) or some words like that. The object itself, plus the texture for it (terobject_building**.bmp, terobject_trees**.tga)
The other alternative would be to make LOD objects, of low polys, and scatter them around the landscape. This is how the trees and such are added on the IcelandNA terrain in SF2:NA.
Some of the ground texturing (roughness, shading) should be able to be done with the noisenormal. bmp (for land). Seas/water/rivers use a waternormal.bmp to create the animated wave action.