How does Chesnutt present the incorporation of folklore in "The Goophered Grapevine" as a method for undercutting white privilege and legitimizing both African Americans' creativity and the efforts of Reconstruction?

In "The Goophered Grapevine," folklore is a source of agency for Julius, a formerly enslaved man who lives on lands essentially abandoned by his former owner.
When the narrator (a Northern businessman eager to invest in the postwar South) meets Julius, the old man tells him that the grapevines in the vineyard he hopes to buy are in fact "goophered," or cursed. Julius explains that the curse goes back to the days of slavery when the owner of the plantation, Julius's old master, had an enslaved woman place a hex on them, condemning anyone who stole the grapes to death or misfortune. He even recounts the story of another northerner who came before the war offering to improve the vineyard. Instead, the vines—along with an enslaved man who had previously eaten from them—died.
As it turns out, Julius has been using the story of the goophered grapevines to ensure that he remains the only person to benefit from them. His story is meant to persuade the narrator to look elsewhere for his investment. Ultimately, however, the man purchases the land, but Julius is allowed to remain as a paid worker, an arrangement that the narrator believes to be "more than an equivalent for anything he lost by the sale of the vineyard."
Julius therefore uses this folklore to carve out a living for himself in the post-slavery world of eastern North Carolina, one that continues even after the land is sold. Like many African-Americans, he has to negotiate his way through the changing landscape of Reconstruction. He is not "undercutting white privilege" so much as he is trying to survive in a world still characterized by it.