Can someone enlighten me to as what the source code would be exactly? Is that different from the game engine?
So, when you write a program you use a programming language, like C# or Python. This lets you use a series of preset commands, and to define your own commands for later use. The source code is basically a text file that contains a whole bunch of words and punctuation in that language that says what you want the program to do under any and all circumstances. But computers aren't very good with words. They need their instructions in as simple a form as possible, which is called "machine code" or a "binary file". Also an "executable file", because the computer can just do what it says. A compiler takes the text file full of words, and turns it into binary instructions the processor can understand. But editing machine code is very difficult, especially for something as big as a full game. Some people can do it, but it's slow, laborious, and prone to devastating errors. Doing enough work to add entire powersets (like adding i24 would involve) is theoretically possible, but the timescale would be immense. Like, decades or more.
The game engine is what makes the game's variables change. It's what rolls to hit, makes a bad guy's HP go down when you hit them with a power, and gives you inf and a chance at drops when you defeat them. The game engine and the game client (which has all the art, maps, effects, text, etc) both have source code, designed to interact in a bunch of ways to let you play the game and see the same world as everyone else. But it's the binary files, the machine code, that actually let them work. So if NCSoft released binaries for the server and client, you'd be able to play, but not edit. If they released the source code, you could edit to your heart's content, but you'd need to find or build a compiler before you could use the modified game code.