I finished the game on hard mode, but I would really like to go back and replay each level with all the guns. I heard you can edit an ini file to get the console, but I find it doesn't seem to work with the gog version for some reason. I've tried it on two different computers so far.

If your playing silent assassin, whatever level you choose you can select which guns you want to use.

I've been wondering about this too. I'm pretty sure you're talking about hitman codename 47.

There is an existing topic about the console not popping up for someone. You can check if the solution I posted there works for you. (It does for me) Otherwise, I'm out of ideas as well.