I tried to rename the bots this is what I did:

I'm using an text editor to open prefs.cs.
Then I search the line with the bot names.
I edit them.
save.

But when I start a game I just see the default bot names.
And when I go to the prefs.cs file again the names chanched to default.

What am I doing wrong?

Everything what you said looks good expect you didn't delete the old pref information. I believe you tried to edit ThinkTanks/game/server/pref.cs file, if so you have to first delete the old saved information of that file before it will accept your new changes. In same folder with the pref.cs file there are a file called pref.cs.dso. Delete that file(pref.cs.dso). Now make your changes, save it and start TTanks and your changes should be working. Note: If you only have.cs.dso file of something, but you don't have the.cs file. Don't ever delete the.cs.dso file, because the game won't generate new one for you without the.cs file. Got it?

Yeah I got it. You helped me again! Your great!