Sorry but a user's Steam ID never changes, it is just totally impossible, not when they're on the server, not when their account is offline, and not when they're just logged into Steam it ever changes.

As for User IDs:
Every time a client connect they get assigned an User ID starting from 2 and counting 1 upwards for every client that connects, a client keeps their Steam ID for as long as they are connected, if the client reconnects to the server he gets assigned a new user ID following previously stated rules. This, aling with the fact that it is always a small number makes it the ideal thing for mods to track a player, so everything ranging from Eventscripts, to Mani and Sourcemod use it.

There is no way either one of them changes for a user while connected to the server, it is impossible.

The User ID is so inherent to the Source Engine, that you couldn't use a hack to change it, because the engine uses it for itself to keep track of a player. if you'd find a way to change (something I'd call impossible too) your userid in mid-session the engine wouldn't know about it since it only cares about assigning user IDs to Steam IDs when a client connects, so the player would essentially be kicked, or the server would crash.

As for the Steam ID, The server never locally remembers the Steam ID, as it almost never needs it. It only needs it a few times, (when a), instead every server keeps a connection open to the Master Game Server. Which it essentially queries for the Steam ID. (in fact it's way more complicated because the client is also involved in this connection, but the point is; it's very secure).
To fool a server into thinking you have a different Steam ID and getting it validated. You would have to be packet sniff the connection and intercept it. Something very complicated, and at the cost of sounding melodramatic something only a serious hacker could do. Hypothetically. Still then you would essentially have to act as the Master Game Server, making the server impossible to connect to for people that are using the normal Master Game Server.

So to summarize:
Changing your Steam ID and User ID while you are connected is impossible in normal circumstances.

Now I'll put that anti name changing mod on, but the most it could do is remember the old name and keep that. It's impossible to prevent the actual name change.

Been there, done that. No regrets, never give up on what's important. Prioritize. Happiness is all that matters.
I really like meowers but can't own any for the time being.

Software Developer with a fondness for Python & UE4. 🐱‍👤

Interested in Star Citizen? - Use STAR-PZ6J-4C62 and get us both some cool extras :3

^ That. You can't change your Steam ID. Plus the guys with name change hacks always have a % at the end of their name, open up the admin menu and you can find them easily.

Let me re-word what I said. I don't remember a single person changing their Steam ID before switching accounts, but as Kharn stated, it's not like we're forgetting our basic admin tech. /ban (steamid) 0 hacking, sm_ban (steamid) 0 hacking, all of that and every time, it would spit out "[SM] No matching client was found."

Kharn claimed to sit in HLSW and watch their Steam ID's change. But, if I can sit in the server and get an error when I try to ban them, I think something is up.

Like I said in Steam =]

Prefix the Steam ID with #
And convert : to _
In console and chat.

Been there, done that. No regrets, never give up on what's important. Prioritize. Happiness is all that matters.
I really like meowers but can't own any for the time being.

Software Developer with a fondness for Python & UE4. 🐱‍👤

Interested in Star Citizen? - Use STAR-PZ6J-4C62 and get us both some cool extras :3

Ok wow savage just after you had left RB I told you about this method I guess you put it to good use! (yes the number one, originally it was going into the admin menu slapping ppl till you find what number they are, then muting them to be sure of the number, then banning, so I guess savage modded my version a bit)

You thought of it, but people were using it before you XD

Probably, but not in RB. In fact the only people I told about the method was savage ad you Stevie, which for you guys it was kinda unhelpful...

Yup, i use a different way and savage probably does to XD

Exactly, to me I think it's easier than finding a stea ID though.