This is for both: single player and multiplayer.
Multiplayer unlocks are actually tied to your "profile.bin". I know this because I tested it and it worked.

1. Make 2 folders. 1 - called 'original' and 2 -called 'changed'.
2. Go to C:\Program Files (x86)\Steam\userdata\########\49540\remote
3. Copy and paste in the folder called 'original', the following files:
a) a file named ''remotecache.vdf'' and
b) a folder called 'remote', as well as a file that's indie of that folder (called ''profile.bin'').
Now you have backed-up original files.

4. Download new profile.bin file [drive.google.com] and paste it in a folder called 'changed'.
5. Untick the game from saving to cloud in steam options.
6. Now that you have backed up files in previous steps, you can go to this path: C:\Program Files (x86)\Steam\userdata\########\49540\remote. After that delete everything from that folder.
7. Next, you have to place that new, downloaded remote folder with all contents that's inside (there is only ''profile.bin'' file). However, DO NOT paste ''remotecache.vdf'' file.
8. Now that everything is in place, all you have to do is play the game. You can check for changes within the game.
9. Close the game.
10. Go to game properties on steam and enable steam cloud, so that it works again.
11. Play freely.

Note: you can use another ''profile.bin'' file that could have everything unlocked for multiplayer, as well as single player. But you'll have to find it on your own.

https://steamproxy.net/sharedfiles/filedetails/?id=1739038595