After downloading the mod, use a program such as 7zip or WinRAR to extract the main folder of the mod.
Navigate to assets/mod_overrides. The assets folder is supposed to be in your game's installation folder (don't know where that is? click here). Create the folder if necessary
Move the main folder of the mod from step 1 to the folder you navigated to in step 2.
For randomizers, paste the contents of the folder in the root of the game (folder that contains "payday2_win32_release.exe") since it adds both mods and mod_overrides.
Warning
When the randomizer is on, it will make the bags invisible to the other players.
You'll also need to assign a keybind to activate/deactivate the mod since it will be off by default at the beggining of a heist.
Install another dakimakura along with the randomizers to have the texture of that respective dakimakura show on the back of the heisters, on the van and when the mod is deactivated, otherwise it will be the default lootbag texture.