Oh hi Firework !
I want to try to give what I know

I use greeting so much from decades ago (uh, not that much x) ...), no, I mean a long time ago

1. Tbh, idk why but I still dunno the exact meaning of this one but, um, "after" ? If its like what I've thinking of then its 'Yes. AFAIK, they will (surely will) see it, even after they joining a room while run a match already, they will get Greeting message when the screen finished loading if I remember correctly (hey! its been weeks from my last game D: )...
2. Answer in-a-nutshell is 'Yes, and the long one is that Greeting message will remain just like before, until the Game Room is removed, even the host is changed though -> This why we must thinking about future effect using Greetings, as well as the used words. Don't use your name
3. If I recall correctly (again), then the way to end Greetings is just using "/greeting " without quotes. Hope works (Once more, its been a long time since my last game xD )...

I love Greetings command, well, I think because nobody else doing it until you came out and asking this xD
At least I know there someone using Greetings command too!
I wonder if everybody else in online Hedgewars using it as well =/
Just like that spammer spamming about "/finish" so everyone know it xD (the problem is, he ruin my room and I believe others as well, and this guy, never stop D_D !!!)
Wait, why I telling these x] nvm! I just guessing everybody using "/finish" to cheat the entire game hehe x)
And, I wish everyone in forum had a great day ^^ !!!

Hi UltiMaxKom,

Many thanks for your reply.

Just to clarify, by *after* I meant this scenario:

1) User joins room (no greeting is set).
2) A greeting is set.
3) Does the user still see the greeting (since it was set after they entered the room)?

Oh, I'm sorry, Its been three days from my last pop-up here, its too busy for me =[ (its reality xD)
For the "after" scene you've explain, now I perfectly understand =/
And oh crap, I did a mistake both to myself and you D:

First of all, I tried it and "I think its worked" but its not (after quick testing (no free time))
Tbh, now idk how exactly the method to use to disable "/greeting " command =(
I just think its work, but I doubting my answer, making me want to test it instead, and it didn't worked not like what I've expecting before =\
And secondly, the after scene have different answer than my last answer above, and its No (but believe me, this time I really sure about my own answer)
The players who already in room before the /greeting is set won't receive the greeting message
Only entering player will receive the greeting

Okay then Firework
I'm sorry for my mistake and I'm late tho =[
Its also a mistake for me to believe that using "/greeting " will work (to disable it), but it doesn't uff...
But anyway, I hope you had have a good day ^^

Thanks for the update.