There's a thread at http://www.modthesims2.com/showthread.php?t=84924 that explains about the userstartup.cheat file, and I tried to use it. I have open the file with notepad, and found this

boolProp testingCheatsEnabled false

So I added my own cheats I inteded to be loaded at the startup, and it was like this

boolProp testingCheatsEnabled false
intProp maxNumOfVisitingSims 8
boolProp allObjectLightsOn true

I saved (the file is still userStartup.cheat, I didn't turn it into txt or something else), moved the back up of the original file somewhere else, and tried. However, it didn't work. The game had crashed while being loaded. Is there something I should take in consideration as well? Or are those cheats unsuitable to be loaded this way?

I know that the max number of visiting Sims works with the user startup cheat, and so does the testing cheats enabled. But I'm a little puzzled as to why you'd want to set the testing cheats off in the user startup- they're off when you start the game, anyway. The only one I'm not sure about is the object lights property, try taking that one out to see if it will work.

The one with the testingcheats at false was there by default, the first time I ever open the file it had that already written, and I didn't consider a good idea to delete that, if the install had included that command in there it must have been for a reason.

I will try with removing the one of the lights

EDIT: Yes, it worked without the one for lights. Well, at least that cheat works here if I use this for making an alias