I never really got to experimenting in the way that you're describing, although the only time I owned a cheat 'device' was when I had an Action Replay disc for Playstation. I was always surprised that certain ridiculous cheats wouldn't just crash the game. I remember you could start out with all items in Metal Gear Solid, get to the first truck (it's about 5 minutes in), get into the back wearing the Snow Field cardboard box, and you'd be prompted to enter the second disc, skipping right to the final portion of the game.
About the GoldenEye cheats:
You could unlock cheats in three ways: by beating levels on particular difficulties within certain time limits, or enter codes (a sequence of button presses/combinations) at different menus, which would add them to the cheat option in the main menu. If you activated any of these cheats, it wouldn't let you progress through the game (you'd beat the level but not progress).
The third method was inputting them after you'd started a mission, which would also allow you to progress. I haven't tested it in a while (I think I may have to later), but I distinctly remember it being very unforgiving about speed of entry, which was enhanced by the trickiness of the sequence of button presses (they took a lot of 'rehearsal'). Scroll down to 'Single Player Codes' and
see for yourself. I'll try them again for myself later.