Can you tell me anything more about this action?

it is a "related mechanism". It was mounted on old pianos, even on some Bechstein. The rod above the repetition lever replaces the roller because it is clearly visible that the hammer rod ends with a wooden knob that would not be appropriate in contact with the repetition lever. Obsolete mechanism!

Thank you very much ?

How do you adjust the hammer-string distance?

by loosening or tightening the two screws in a coordinated manner.

Thank you!!!