Here's the paragraph of hints, with the key words in bold:

Keeping this in mind, I'd like to begin by talking about our weird lives. Each stage can be so free, except when the clock is ticking and the debug process is so hard you just want to say "Owwww!" I'm not paid enough money for this abuse; 57695 dollars wouldn't even be enough. I'd rather just watch TRON.

To derive the codes, translate the key words into numbers using the letter/number associations on a telephone. Like this:

ABC=2
DEF=3
GHI=4
JKL=5
MNO=6
PRS=7
TUV=8
WXY=9

With that in mind, here is the complete list of cheat codes. Entering a cheat code (except for the last two) will permanently unlock its option on the Extra Options screen. The cheat will not be active by default. To actually use the cheat, go to the Extra Options screen and set its option to "Yes."

CodeFromNamePurpose
5769557695Color SelectAllows you to change the gameplay colors (walls, player, background)
3825?Allow ProfanityCertain combinations of initials will no longer be "censored."
3733freeFree PlayYou may continue an unlimited number of times. Credits option will be ignored.
25625clockInfinite TimeYou may take as much time as you need to finish each level.
78243stageStage SelectYou may select any of the 30 levels to begin play on. This works for user-created levels, too.
93473weirdReverse ControlsLeft becomes Right, Up becomes Down, and vice versa... good luck!
33284debugDebug ModeUgly-Looking Debug Mode appears at game start. I used this for testing during development.
69999OwwwwManiac ModeNibbles2 will not wait 1/18th of a second before drawing the next frame. This makes gameplay impossible except on really slow machines.
8766TRONTRON ModeThe end of your snake will not be erased. This makes retracing your steps impossible. How far can you get?
23446beginNovice ModeUpon crashing into a wall, you will have a few seconds to change direction before actually losing a life. Essentially, you can't die unless you trap yourself.
54837lives9 livesThe Lives option will now go up to 9.
66639money9 creditsThe Credits option will now go up to 9. Note that Free Play makes this code pretty useless.