Hi there, I figured out how to remove the undesireable reflections without need console commands.

First, extract the gma by drag+dropping it onto gmad.exe (in garrysmod/bin/gmad.exe)

Then go into the following files and delete the following lines:
"$envmap" "env_cubemap"
"$envmapcontrast" 1
"$envmaptint" "[1 1 1]"
Files:

\materials\models\monster\lavasat\lavasat_metal.vmt

\materials\models\monster\cromcruach\cromcruach_metal.vmt

\materials\models\monster\cromcruach\staff_cromcruach.vmt

\materials\models\monster\dullahan\dullahan.vmt

(You may also want to add $nocull 1) to this one^

\materials\models\monster\dullahan\dullahan_rock.vmt

\materials\models\monster\grimreaper\grimreaper_altheron_metal.vmt

\materials\models\monster\grimreaper\scythe_grimreaper_altheron.vmt

\materials\models\monster\habitant\habitant_metal.vmt

\materials\models\monster\juggernaut\juggernaut_metal.vmt

\materials\models\monster\lughlamhfada\lughlamhfada_upper_metal.vmt

\materials\models\monster\lughlamhfada\lughlamhfada_foot.vmt

You should probably also remove the extra close brace from this one ^

\materials\models\monster\lughlamhfada\lughlamhfada_hand.vmt

\materials\models\monster\lughlamhfada\lughlamhfada_head.vmt

\materials\models\monster\lughlamhfada\pc_male_lughlamhfada_lower_metal.vmt

\materials\models\monster\lughlamhfada\spear_lughlamhfada.vmt

\materials\models\monster\lughlamhfada\sword_lughlamhfada.vmt

\materials\models\monster\meer\meer_trans.vmt

\materials\models\monster\ogre\hammer_blackhammer.vmt

\materials\models\monster\ogre\blackhammer_armor.vmt

\materials\models\monster\ogre\knuckle_bloodfist_diffuse.vmt

\materials\models\monster\ogre\orge_jirkal_armor.vmt

\materials\models\monster\ogre\ogre_rage_metal.vmt

\materials\models\monster\ogre\ogre_titan_armor.vmt

\materials\models\monster\yulkes\yulkes_foot_metal.vmt

\materials\models\monster\yulkes\yulkes_hand_metal.vmt

\materials\models\monster\yulkes\yulkes_lower_metal.vmt

\materials\models\monster\yulkes\yulkes_upper_metal.vmt

\materials\models\monster\yulkes\yulkes_helmet.vmt

Hopefully the author sees this and updates the addon...