To start editing, you need specialized software capable of decrypting and re-encoding the game's proprietary formats (typically 413 or 121 headers).

He clicked on his desktop and launched a specialized, community-made program: L2 File Edit

You cannot open L2 files with a standard text editor like Notepad. Most files in the /system folder are encrypted. To get started, you’ll need:

Most private server owners explicitly allow or even encourage client-side editing, as long as you don't use it to exploit (e.g., removing wall textures to see through them). Always check the server’s rules.