Is it permissible for a suitor of good character and religious commitment to propose to a girl, but her guardian rejects him due to tribal reasons, customs, and traditions, so she falsifies his identity and nationality before the guardian to prevent rejection, or marries him in court and informs the guardian later?

If the suitor is a man of piety and good character, your guardian (wali) has no right to refuse his marriage without a legitimate Shar'i (Islamic legal) reason. A guardian's refusal of a suitor merely because he is from another country is a clear mistake and a form of 'adhl (unjust obstruction of marriage) that nullifies his guardianship. Try to persuade your guardian and intercede with someone who influences him, and supplicate frequently. If he insists on refusing, refer the matter to the Shar'i judge. It is not permissible for the suitor to change his name or nationality, as this involves deception and fraud, and due to the severe warning that results if it leads to claiming lineage from someone other than his father or tribe.