Credence's new style in Fantastic Beasts 3 mirrors Snape's, thus portraying him as the antihero with noble intentions and spoiling Credence's ending.
Fantastic Beasts: The Secrets of Dumbledore shows Credence Barebone (Ezra Miller) wearing shoulder-length hair and dark clothes that mirror Snape's (Alan Rickman) style in Harry Potter, thus spoiling Credence's ending in the five-movie saga. Fantastic Beasts 2 came with a major plot twist, as Gellert Grindelwald (Johnny Depp/Mads Mikkelsen) revealed Credence's identity as Aurelius Dumbledore, a fourth Dumbledore sibling. Credence seems to embrace his newly-found identity in the third Fantastic Beasts installment by changing his style - its uncanny similarity to Snape's style is not a coincidence.
Severus Snape is arguably the most complex character in the Harry Potter series, being portrayed as a villain for most of the seven books before J.K. Rowling revealed his undying love for Lily Potter and loyalty to Albus Dumbledore. By The Deathly Hallows, Snape becomes the true Harry Potter antihero. He protects Harry (Daniel Radcliffe) out of the selfish need to assuage his self-loathing at having been partially responsible for Lily’s death. Snape's work to defeat Voldemort is similarly driven by his guilt and need for vengeance against the man who murdered Lily. While Snape is seen through Harry's eyes and only revealed as the antihero late in the saga, Credence is introduced in Fantastic Beasts And Where To Find Them as the antihero.
As a child, Credence was constantly abused by his adoptive mother, Mary Lou Barebone (Samantha Morton), and tortured by the Obscurus, which possessed Credence because Mary Lou forced him to suppress his magic. Throughout the two Fantastic Beasts movies, Credence is manipulated by Grindelwald, who believes only Credence is powerful enough to defeat Dumbledore (Jude Law). Credence joins Grindelwald at the end of Fantastic Beasts 2, but Queenie (Alison Sudol) senses "he's not sure he made the right choice." With Grindelwald's violence rising and his lies becoming more transparent, it's likely that Credence, just like Snape, will abandon his allegiance to the dark wizard and join Dumbledore, helping him end Grindelwald’s reign. Credence's obvious Snape-like style in Fantastic Beasts 3 spoils his character arc by mirroring an all-too-familiar Harry Potter antihero.
Grindelwald has been abusing Credence's need for an identity, telling him whatever he wanted to hear in order to secure his loyalty in his war against Dumbledore. It's even possible Grindelwald lied about Credence's identity as Aurelius Dumbledore, making Credence feel like an outcast, rejected by Albus, feeding his fear that he is unwanted and manipulating him into believing he wants to fight Dumbledore for himself (not for Grindelwald). But Grindelwald is only using Credence for his extreme Obscurial power, which manifests in moments of great distress. It's only a matter of time until Credence confirms his doubts about Grindelwald and switches sides - much like Snape, who once joined the Death Eaters, did when he started the arduous task of being a double agent for Dumbledore.
The Fantastic Beasts 3 trailer shows Credence fighting Dumbledore in an epic (and highly destructive) battle, so Credence's character change will most likely be a slow one. But Credence has just left his close friend Nagini behind (just like Snape once abandoned Lily for the Dark Lord), and similarly to Queenie; he is stuck with Grindelwald as he feels he is the only one who can give him a sense of belonging. Changing loyalties might be a recurrent theme in Fantastic Beasts: The Secrets of Dumbledore, and in Credence's case, it's his new Snape style that predicts his antihero character change.