Wrong section but I'll help as you seem to be new here.
You only need to add definition opcodes for newer revisions, let's say Jagex added a new opcode for item lighting. Now you gotta download a deob that has item lighting opcode added, because you'll need to know what's the opcode's index and what data does it read. And let's say It's something like this:
Code:
if (opcode == 1337)
item.itemLighting = stream.getShort();
Now this example gets the opcode 1337 of the item definition once It's found. It defines the item's lighting to the buffered data, get short, or get signed short.
There's an easier way to find opcodes is by printing out all unknown/undefined opcodes.
Hope this helps.