Is a person's changing of their name and tribal affiliation—with the tribal elder's approval—in order to obtain work in another country considered tampering with lineage and an act forbidden by Islamic law, knowing that this work is essential for him to support his family, and his father is aware of this?

This act is unequivocally forbidden, due to its implications of attributing oneself to a father and tribe other than one's own, involving lies and forgery, and the resulting invalid matters concerning inheritance and mahramiyyah (unmarriageability due to kinship). There are ahadith that prohibit claiming lineage from other than one's father, and threaten those who do so with Hellfire. Therefore, it is incumbent upon anyone who commits this act to repent, destroy the forged documents, and attribute themselves to their real father and tribe. It is not permissible to bear witness to anything unless one has knowledge of it, and false witness is forbidden, and forging a place of birth is forbidden, so how much more so is changing one's lineage and tribe. The absence of work, or family support, or the father's knowledge does not justify this great reprehensible act.