okay so I completely redid the code. I just need to figure out if there is something that returns the vector of a vertex. Also after the terrain is deformed the player can just move through the new part of the ground as if the old ground of the terrain was still there. Any suggestions?

Code:
///Change Terrain
                VECTOR pos1,pos2;
		vec_set( pos1 , vector(mouse_pos.x,mouse_pos.y,0) );
		vec_for_screen (pos1, camera);
		
		vec_set(pos2 , vector(mouse_pos.x,mouse_pos.y,10000));
		vec_for_screen (pos2, camera);
		
		c_trace (pos1.x, pos2.x, IGNORE_ME | IGNORE_CONTENT | IGNORE_SPRITES | IGNORE_MAPS | IGNORE_PASSABLE | IGNORE_MODELS | IGNORE_FLAG2 | SCAN_TEXTURE); 
		
		
		if (HIT_TARGET && you && ent_type(you) == 4) // click onto terrain
		{
			var vertex_num1 = ent_nextvertex(you,hit.x);
			CONTACT* c1 = ent_getvertex(you,NULL,vertex_num1);
			var vertex_num2 = ent_getvertex(you,NULL,vertex_num1 + 1);
			var vertex_num3 = ent_getvertex(you,NULL,vertex_num1 + 66);
			var vertex_num4 = ent_getvertex(you,NULL,vertex_num2 + 66);
			draw_point3d(hit.x,COLOR_RED,100,5);
			if(mouse_left){ 
				c1.z = my.z + my.min_z;  // increase the vertex height
				c1.v = NULL; // c.x,y,z was changed, instead of c.v   
				ent_setvertex(you,c1,vertex_num1);    // update the mesh
				my.z = c1.z - my.min_z - 1;
				wait(-1); // reload
			}
			
		}

boolean my.awesomeness = so true;