A walkthrough at last.

[forlik]

hb2, very good, keep it up!

Just a couple of remarks:

Originally Posted by hb2

9. You have your chance when he enters an empty corridor. Kill him right away.
10. Carry his body into the nearest guest room. Leave the body behind the armchair in the sitting room (red circle in the map above).

A good chance to kill the traitor in his room. I don't remember the number, but it on the second floor.

Originally Posted by hb2

11. Regardless of where you killed the traitor, to continue now you need a hotel staff disguise. There’s a guard standing by this same hallway, by the large open doors at the start where you just entered. You must kill him cleanly, though, so run by him quickly to lure him out. You may have to try several times. As soon as he walks into the hallway to check on the noise, sneak behind him and kill him cleanly, pretty much in the same spot as you killed the traitor (if you killed him here).

Cook uniform can be used also, but waiter uniform - can't be used
Maybe I will fix it in additional MoTmod versions.

Originally Posted by hb2

13. Optional task: finding the weapons.

Is there any sense to remove knife and fiber wire from player's inventory and put all of these (perhaps with chloroform) to the weapon's place?

Originally Posted by hb2

17. Enter sneak mode so you won’t be seen. Kill the guard by the door with a knife throw when he isn’t looking. You must be very quick.

You can stun this guard also. You will get 1 stunned instead of 1 killed.

[Liz Shaw]

Originally Posted by forlik

You can stun this guard also. You will get 1 stunned instead of 1 killed.

You can also throw a fragile object (eg. glasses and cups) at the guard if you aim for his head. But don't try it in MoTMod, for some reason the guards in the other room will investigate the noise...

Also, the waiter's suit CAN be used. Maybe you're referring to the manager's suit...

hb2, security guards, cooks and waiters are all of the type "Soldier", meaning you can use one of these disguises to get into the diplomat's room easily.

[forlik]

Originally Posted by Liz Shaw

But don't try it in MoTMod, for some reason the guards in the other room will investigate the noise...

Try to close doors before the guards and select a position to throw as far as possible from the closed door.
It's possible:

Originally Posted by Liz Shaw

Also, the waiter's suit CAN be used. Maybe you're referring to the manager's suit...

My mistake, sorry
This suite confused me:

[hb2]

Thank you both for the replies! I'll amend the solution accordingly and credit you. I hadn't tried the cook outfit. Duuuuh me!

forlik, how do stuns and object throws (as opposed to killing) affect the aggression rating? And is the killed vs. stunned ratio in the mod related to the aggression rating?

[forlik]

Originally Posted by hb2

forlik, how do stuns and object throws (as opposed to killing) affect the aggression rating?

It depends on several factors. You can investigate it by yourself. Just save before enemy and use cheat "complete" after kill or stun.
For example (hard difficulty) if you kill cook, you aggression will increase by 10%, if you stun him - by 3%.

Originally Posted by hb2

And is the killed vs. stunned ratio in the mod related to the aggression rating?

Yes. I've not changed the rating calculation in MoTmod, so MoT algorithms are used.

[forlik]

Originally Posted by Liz Shaw

You can also throw a fragile object (eg. glasses and cups) at the guard if you aim for his head. But don't try it in MoTMod, for some reason the guards in the other room will investigate the noise...

Originally Posted by forlik

Try to close doors before the guards and select a position to throw as far as possible from the closed door.

It seems the player's position to throw doesn't matter.
I've tried to stun the diplomat's guard from the position between the closed door and the guard on hard difficulty level. After 2nd attempt I've catched a luck

[OSS]

Originally Posted by forlik

It seems the player's position to throw doesn't matter.

Yes. It doesn't matter where you stand. Position where object hits the target is matter.

[pacbman]

I opened the safe but there is no option to remove documents. Was I supposed to get documents from somewhere?

[Liz Shaw]

Originally Posted by pacbman

I opened the safe but there is no option to remove documents. Was I supposed to get documents from somewhere?

Perhaps you should wait until after the diplomat makes it back to his room after getting the documents in the library. You could fill out the time by finding the hidden weapon and/or killing the traitor.