Oki, so server can't do it himself.

I know about the easy achievement stuff, I was curious if it's possible to make mod which let's you to unlock those achievements in legit way instead of messing with ingame hosting.

As I said, you would have to write the ID in a file, the dedicadet server itself can not find his owner. You could easily unlock any archivment, but I would not participate in such mods.

It was just my curiosity. "Did modder beat dev?"
Dev doesn't want us to unlock host achievements on dedicated server because he doesn't know how to check host.
That's why I wondered if it would be possible with simple mod.

"so others can't fake his ID" thats exactly what the mod did.
"mark this player as "host"" i can make this possible so you can add your id to mod settings, but what should it bring except appearance?

Would it be possible to distinquish which player hosts dedicated server with this? (after modifications)

Find steam ID of person who started dedicated server and check steam ID of people who join, if player who joined has the same steam ID as person who started server, then mark this player as "host" + remember that this player is a host so others can't fake his ID?