How to add terrain in a specific location in RMS scripting in DE

I like the map snakepit but I don't like how the opposite team can raid you in the lake. I would like to stop this by adding a forest that cuts in the lake in two as evenly as possible. I am experienced with age of mythology RMS but not aoe2 RMS.

The problem I am having is that create create_terrain doesn't allow me to choose the location of the terrain to be in the center of the lake. My current solution is to add a forest in the lake without specifying the location but it often doesn't divide the lake evenly. I know that if I use create_land I can control the location of the area but when I add this to the RMS script it completely messes up the map (the lake disappears, the players are in completely random places, and the forests don't show on the mini-map). I think that this is because Snake pit is a special map which doesn't allow for land generation

Please tell me if there is a way that I can add the forest in a specific location without messing the structure of the snake pit map.