Ok so this isn't 100% right, but i'm pretty sure this might be the problem to why the ability or any other hack doesn't work.
Ok so I think that the reason to why the ability hack doesn't work is because EA probably put a Size lock on it. Meaning if the ratio, packed size, or the size changes, then it will display the "Invalid Client Data (6)" error.
Here is what happens:
1. So i'm going to try to make the ability hack. And before I start here is a picture showing the ratio, packed size, and the current size of the DefaultCustomization.xml file.
2. Then I, wanted to leave the size the same, so instead of adding to the "equipment" line, I just replaced this:
with this:
3. Then I saved it, and took a look at the size, it was the same... But then look at the ratio and packed size:
4. Then I tried changing ;1234 back to ;2001, and look still the same size as to when I replaced it with ;1234. Except the Packed Size Changes.
5. Now even with the ;2001, try going in game. It will most likely start. Now try getting on a server. You'll get a "Invalid Client Data (6)" error.
Now, the size is the same. What the hell is wrong then.
The ratio changes and the Packed size of the file also changes.
So all we need to do is find a way for it to stay exactly the same.
Now i'm not saying this Reasoning to why the ability hack doesn't work is 100% true.
But it's a really good one.