If the pilgrim who is doing tamattu’ is not able to do ‘umrah before Hajj, then he should change his intention from tamattu’ to qiraan, and intend to do Hajj and ‘umrah together.
This is what happened to ‘Aa’ishah (may Allah be pleased with her). She was doing tamattu’, then her menses came and she was not able to do ‘umrah before Hajj, so she joined Hajj with ‘Umrah and it became qiraan. This was narrated by al-Bukhaari and Muslim.
It is not permissible for the pilgrim who is doing tamattu’ to change his intention to ifraad, because when he intended to do ‘umrah, it became binding upon him to complete it, because Allah, may He be exalted, says (interpretation of the meaning): “And perform properly (i.e. all the ceremonies according to the ways of Prophet Muhammad صلى الله عليه وسلم), the Hajj and ‘Umrah (i.e. the pilgrimage to Makkah) for Allaah” [al-Baqarah 2:196].
The meaning of ifraad is that the pilgrim will not do ‘umrah; rather he will do Hajj only. Based on that, your changing your intention to ifraad is not valid. Thus your Hajj became qiraan and you have to offer the hadiy.
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) was asked about a group of young men who were afraid that they would not be able to do ‘umrah before Hajj, so they changed their intention to ifraad. He replied:
If the intention was changed before entering ihram, then there is nothing wrong with that. But if it was after entering ihram, then their Hajj became qiraan and not ifraad. What is meant by it being qiraan is that they joined Hajj with ‘umrah, because qiraan takes two forms:
1. When the pilgrim enters ihram for Hajj and ‘umrah together when he first enters ihram
2. When he enters ihram for ‘umrah first, then joins Hajj to it before starting tawaaf.
Based on that, so long as you entered ihram for ‘umrah first, then you decided to make it Hajj, you were doing qiraan. If you slaughtered a hadiy on Eid al-Adha during your Hajj in that year, then you have done what was required of you and have completed your Hajj and ‘Umrah. If you did not slaughter a hadiy, then you have to do so now, and eat some of it and give the rest in charity. If any of you cannot find a hadiy – i.e., cannot afford to buy one – then he must fast for ten days now. End quote.