So, at level 6-9, will there already be a Special Ability? Isn't that a bit too overpowered?

This mod will allow you to avoid taking a bunch of unnecessary skills on the way to obtaining a Special Ability.
Yes, it sounds a bit like cheating, but if you think about it, all races have quite good Special Abilities, and everyone will be able to get them.
As for the implementation, I've seen more complex mods on this forum.

Added 5 minutes later

Here's a link to the mod: http://heroescommunity.com/viewthread.php3?TID=38410

The thing is, this mod is not localized into Russian, and it will be difficult, if not impossible, for a person who doesn't know English to understand it.

Added 5 hours 20 minutes later
I've done everything. Here's the link to the mod: https://yadi.sk/d/qHwb0bmtrPRha.
I came up with it myself, I made it myself, I uploaded it myself – that's what I call a request system. =)
By the way, I advise aspiring modders to explore other mods to get acquainted with the structure of the data archive.