Does work built upon a certificate obtained through bribery become permissible years later, after repentance, remorse, and mastering the work, following a previous fatwa that allowed it?

Applying for a job with a forged certificate is definitively unlawful (haram (definition)), and this action is a devilish trick and a commission of clear forbidden acts. Committing a sin with the intention of repenting does not intercede for its perpetrator. Allah has never made disobedience to Him a cause for good, ever.

As for the issue of the salary of an employee with a forged certificate after repentance and mastering the work, it is subject to different interpretations: Sheikh Ibn Baz: He holds the view that the salary is permissible with repentance if the employee performs his work diligently. Sheikh Ibn Uthaymeen: He was hesitant and held the view that the salary might not be permissible if it was based on deception in the final certificate, especially if the job required what was cheated in. However, he hoped for permissibility if the repentance was sincere and the deception was in a subject unrelated to the job. He stressed that deception is forbidden in all cases. He clarified that cheating in exams is among the major sins, and it results in taking a salary unjustly.

A forged certificate is greater and more severe than a certificate that involved cheating in its exams.