In previous versions it was really easy to change my name / nick for playing LAN games but the console name command no longer does anything. It looks like it's hard coded to some GOG assigned name. I want to do this offline as these are LAN games, not online/wan.

The general use case is I take my laptop to a different house and assign a different name and/or clan name before we start up a lan session.

How do I change my name / nick for playing LAN games?

And what nick you have in offline build LAN mode by default?
O dont have q2 here. I can guess it is use GOG Galaxy appdata folder inside windows user folder. There is game settings folder and inside is account0. So its looks like galaxy account but with accID 0 and game refer to it. Some offline settings/saves also can be stored there.

If so. Settings inside account0 and in parent folder can be edited by good one text editor (WordPad is good but unavailable for Win10+, use Notepad++) or hex-editor (HxD). You can change id for no reason and maybe there is a way to change name.
Also look to general game settings inside user folder documents|saves. Put name "Playername" directly there probably still work.

Have you ever managed to find a method to change your LAN name? I'm having the same problem right now and it's quite annoying.

Create a BAT file with the text editor (for example Quake 2 MP.bat) inside the game folder and put the following inside: Save the BAT file and launch the game through it.

I had the same question some years ago for the game Blood: Fresh Supply and DustyStyx helped me getting it to work this way.
I'm pretty sure you can't change the name when the game is currently running.

Try the "seta" command in config file or console.
Example: seta name_0 "YourPlayerNameHere"

EDIT: Sorry, I just realized this does not persist after game restart :(