There are many cheats which change the players/characters heads.
Sebastian puts crabs on the heads of players.
Smaug replaces it with stone dragon heads.
Geek replaces the head with the "dreenk" advert mascot.
orwell replaces heads with horses pigs and rats based on the type of character.
There is also a cheat that nullifies this, those cheats are not documented anywhere it seems and there is a separated cheat which acts like loaded (here loaded is just like allammo instead), ah "postal" it was. "dopefish" is like "bigtime" in the late 1996 unreal beta demo
so it combines multiple cheats but this is for example mentioned already in gamesrader etc. Gamesradar.com
Ah apparently Gamefaqs.gamespot.com
the gamefaqs article is a little more complete.
But it doesn't mention everything still.
There was also a lobster one for the heads.
I will edit this article later once I check the game files for clarification and cheats I forgot.
EDITED: The ones I forgot were nexttune, which is useful to bind, this game has directly command bind which supplements set input. The lobster one was...now I don't remember again. I need to write things down this is terrible. Clearcheatheads resets the heads. Setheads name sets it to specific head name. Just looked up the lobster, it is "Pedro", but setheads lobster works too. Offwiththeirheads makes everyone loose their head (lol). usetheforce sets foprce on, digitaloo enables debug mode, haven't tried those two yet. hurtme and healme with amount/rate. Playogg with several things can play external ogg music...that's about it for the useful stuff realy its much more than the faq tell you though.