There aren't any cheat codes that I could find for Deus Ex: Human Revolution. With some exceptions (Saints Row: The Third comes to mind), cheat codes aren't as popular these days.
With the rise of the achievement, people are more interested in playing the game legitimately to get the achievements than cheating. The two systems don't tend to coexist well, as cheat codes would nullify the "value" of achievements. Most games that allow you to cheat disable achievements when you do, for that reason.
The two systems do tend to have the same effect, by extending the length of the time you'd spend playing the game. Which is "better" is completely dependent on what you like, so it's not really a question we can discuss or hope to answer here.
Trainers can sometimes be a bit suspect. They modify memory locations used by the game, which means they need pretty thorough access to your system in order to work properly. Whether allowing that is worth the risk is a call you're going to have to make yourself, I'd say. Since it sounds like you're on a PC, there might also be save file modification tools around, which might effectively allow you to cheat in the game. These are a bit safer, but not totally without risk.