DeveloperMode

This information came from Wormbo following discussion on Uniquely Identify A Player

While each UT installation has a unique GUID (= PlayerIDHash, = CD Key) certain actions by the user will cause the client to go into "Developer Mode" and change its GUID to 5857a730-b66505da-430f3bef-2b845c38.

Only SET commands affecting non-config properties of actor (sub)classes, which can only be executed offline, will change the GUID.

Example

Start UT2004, go to the Settings → Game menu and note the GUID – It will always be the same. If you check the source code you'll find out it's read from GetPlayerIDHash(). Now if you restart UT2004 and type e.g. "set Pawn bHidden False" at the console before going to Settings → Game you will notice it now displays 5857a730-b66505da-430f3bef-2b845c38 instead of the usual GUID.

You can restart UT2004 and it will show you the usual GUID again. On the other hand, if you execute the console command "set Input Space Jump" you are changing a config property of a non-Actor class. This will not change the GUID.

Rationale

Default properties will stick unless the class with the modified default properties is garbage-collected. These changes can persist into online play, which was widely abused in UT2003 and led to Wormbo developing Anti TCC in an attempt to detect these changes.

With UT2004 Epic added the GUID change for problematic SET commands, which puts the client in "developer mode" and blocks it at the masterserver level, at least in the server browser. That specific GUID is also blocked by Anti TCC, SafeGame and UTAN Ban #1971.

Discussion

Sweavo: pasted directly from Wormbo's comments and dressed up / edited by me.