Is it permissible for a girl to marry a Muslim young man of good character who proposes to her, despite her father’s refusal due to differences in some customs and traditions between them?

The standard for compatibility in marriage is religious commitment and good character, not the agreement or disagreement of customs. The guardian (wali) is a condition for the validity of the marriage, so try to convince your father and mediate through relatives and religious people. If that does not work, then it is better to obey your father and forgo marriage to this man, unless you will suffer harm. However, if harm results from this, the matter can be taken to the Sharia courts, because in this case, the father is considered to be preventing the marriage unjustly (a'dhil).