1) add to ext_config.ini:
[MODEL_REPLACEMENT_...]
DESCRIPTION = hide barrier
ACTIVE = 1
FILE = ?.kn5
HIDE = Object10, box_child010, box_child011, box_child012, box_child013, box_child014
If it doesn't work, try with:
[MESH_ADJUSTMENT_...]
IS_ACTIVE = 1
MESHES = Object10, box_child010, box_child011, box_child012, box_child013, box_child014
IS_RENDERABLE = 0
2) add the following section to surface.ini
[SURFACE_xx] ;replace "xx" with the last number section + 1
KEY=08WALL
FRICTION=0.98
DAMPING=0
WAV=
WAV_PITCH=0
FF_EFFECT=NULL
DIRT_ADDITIVE=0.0
BLACK_FLAG_TIME=0
IS_VALID_TRACK=1
SIN_HEIGHT=0
SIN_LENGTH=0
IS_PITLANE=0
VIBRATION_GAIN=0
VIBRATION_LENGTH=0