I wanted to ask if this was in any way possible, because I saw that in a BOP world, where the different kind of dirts generate I couldn't use earthbending on those blocks.

The other thing friends and I noticed is that on our SMP Server the Key Bindings in the Skils Menu have to be reassigned everytime you start the Game anew, is that a known bug, or are we doing anything wring maybe?

As far as I know, if using the config doesn't work, it's not possible, as Biomes o Plenty or I would have to mess with mod loading order.
What version of the mod are you using?
What version of forge?

Forge 14.23.3.2675
Avatar Mod a5.2
BOP 7.0.1

So it would be possible to add blocks via the config?

I just thought, wouldn't it maybe be possible to use oredict entries for determining the blocks? I don't know a lot about this stuff, but like saying, everything that is registered as block:dirt or sthg like that can be earthbended?

Try downgrading to 14.23.3.2611 or 2555.
Also try using a5.3.

Yes, it's possible. Yes, everything that has block:dirt as its name can be bent (bended?).

I did test and it works, at least for me. (Using the config)

@Burgerism
Try seeing if it works with the latest updates
It should work

The blocks thing should, anyway

Suggestion is implemented, bug is known. Therefore, I will close this now.