Dein seems to be the genitive old-fashioned form of the second person personal pronoun in singular, thus the old-fashioned form of deiner. The end of Goethe's Prometheus is
Und dein nicht zu achten,
Wie ich!
He is referring to Zeus. The transformation to modern German, only for purpose of comprehension, would be in two steps, I guess: First, take the old dein to deiner; secondly, transform deiner to the usual accusative form dich.
My question is, whether the second transformation is possible without loosing information (of course, style is lost). Whether Dich nicht zu achten says the same, or this dein rather means "to scorn every possible aspect of you". Or whether the only possible transformation to modern German would stop at the first step (deiner nicht zu achten)?