Replace files in:
Grand Theft Auto V\mods\update\x64\dlcpacks\patchday10ng\dlc.rpf\x64\models\cdimages\weapons.rpf\ 

if you want to replace the luxus version add the tag "_luxe" to all files:

"w_ar_assaultrifle_luxe"
"w_ar_assaultrifle_luxe_hi"
"w_ar_assaultrifle_luxe+hi"
"w_ar_assaultrifle_luxe_mag1"
"w_ar_assaultrifle_luxe_mag2"