The Extensions Directory is a custom modified version of Mosets tree.
Some functions exists as standard, and some functions must be created for example, from the "custom fields". In the Mosets Tree code, you create buttons that connects to those fields. It isn't so difficult if you understand a little PHP.
Mosets has an
own forum dedicated to their products. I recommend you look through the posts there and ask the other users. Maybe you'll get some hints where to change. You can also find a forum dedicated for 3rd party addons and Custom Jobs. Hope it helps!