I have seen the site before, however I don't care for trophies/achivements and the negatives associated with them and consider them a net negative for game design.
As far as ROM hacking goes... I would argue 90% of them are probably sideshoots of basic cheating (I don't know offhand what level of scripting there is available but basic would elevate it a tiny bit), on the other hand the more advanced cheat makers I find to be some of the best applied assembly hackers going.
Anyway games seem to do various things for cheating.
1) Completing levels. There will be a level counter, marker... in the game somewhere. If it changes you have completed a level. If credits screen is playing then you completed the game...
2) Kill counter/combo counter, high score in a playthrough. Fairly obvious really. Similar story for times spotted in a stealth game.
After this you want to be able to chain things together. If health does not go below a value (or change as the case may be) and the level counter goes from one to the next then "trophment unlocked, no damage in level ?". Similarly "did not use ? item/weapon" is possible by similar things.
About the only ones you will truly struggle are the only ones I find remotely interesting, that being the "viral" online ones like played with devs or played with one that played with... that and timers if you are doing longer/multiple plays with a game that does not keep them, though that should be a function of the logic really.
This covers basic boring completing the game trophments, high score, some odd play style (used every weapon without a counter is harder though not impossible, and carried useless item because we thought it funny is also possibly harder but maybe not if it is just an inventory thing).
If it all sounds quite basic it is probably because a lot of it is, it is also why I found Sony's getting a patent for it the other year to be a nice example of the failures of the US patent system.