He intended to do Hajj for himself, then he decided to change his intention and do it on behalf of a relative of his. Is it permissible for him to do that?

Once a person has entered ihraam for Hajj on his own behalf, he does not have the right after that to change it, whether en route to Makkah or in ‘Arafah or anywhere else. Rather he must complete it on his own behalf, and not change it to be on behalf of his father or his mother or anyone else. Rather it becomes obligatory upon him to complete the Hajj that he started, because Allah, may He be glorified and exalted, says (interpretation of the meaning): “And complete the hajj and ‘umrah for Allah” [al-Baqarah 2:196]. If he entered ihraam to do Hajj for himself, then he must complete it for himself, and if he entered ihraam to do Hajj on behalf of someone else, then he must complete it on behalf of someone else, and not change his intention after entering ihraam, if he has already done Hajj on his own behalf, and the same applies to ‘umrah. End quote.

Shaykh ‘Abd al-‘Azeez ibn Baaz (may Allah have mercy on him).

Majmoo‘ Fataawa Ibn Baaz (17/78).