Editing game files manually can be a mixed bag—exciting but risky. I've tinkered with 'GTA V' files before, mostly to mod cars or tweak physics, and it’s wild how much you can alter if you know what you’re doing. The 'fichier' (assuming you mean save files or configs) are often in plain text or XML, so tools like Notepad++ work. But backup everything first! I once corrupted a save by misspelling a value and had to replay 10 hours. Rockstar’s updates also sometimes reset changes, so it’s a temporary thrill unless you’re deep into modding communities where folks share safer methods.
For deeper edits, like scripting or asset swaps, you’ll need specialized tools like OpenIV or Script Hook V. These let you peel back layers of the game without breaking it. I remember adding a flying Delorean mod—absolute chaos, but worth the effort. Just remember: online modding can get you banned, so stick to single-player experiments. The freedom to reshape 'GTA' is part of its magic, but respect the game’s ecosystem too.