You don't 'hack' replays, it's a simple process that anyone can do.
When playing a replay back, press ctrl+p to pause, then ctrl+e to edit the replay from whatever frame you pause it at.
So essentially, you can make your replay as awesome as you like depending on the time youre willing to spend on it. :3
Hope this helped.
I thought that at first but then I saw his post count and thought it was a bit advanced for a junior member to be messing with.
If he was referring to it, then GL to him.