Installation:

1: Install this mod:
https://www.gta5-mods.com/vehicles/mtl-cerberus-200-300-add-on-liveries-template

2: Place the texture from the "Cerberus 300" folder into "C:\Program Files (x86)\Steam\steamapps\common\Grand Theft Auto V\mods\update\x64\dlcpacks\cerberus4\dlc.rpf\x64\vehicles.rpf\cerberus4.ytd"

3: Place the texture from the "Cerberus 200" folder into "C:\Program Files (x86)\Steam\steamapps\common\Grand Theft Auto V\mods\update\x64\dlcpacks\cerberus4\dlc.rpf\x64\vehicles.rpf\cerberus5.ytd"
(N.B. The textures can be renamed as appropriate if extra liveries are already present)