Am I sinful for my Hajj changing from Tamattu‘ to Qiran due to an unforeseen circumstance, and is the money I was given as a reward lawful despite this change?

The Hajj is valid and is performed on behalf of the person for whom the pilgrim is deputizing. If the deputy returns any part of the compensation, that would be more cautious, unless he is permitted to keep all of it.

If someone hires a person to perform Hajj as a Mutamatti' (performing 'Umrah then Hajj), but then the person performs Qiran (combining 'Umrah and Hajj): - Shafi'is: He has added good, and there is nothing against him if he performs the actions for both rituals. If he does not specify the actions for both, he should reduce some of the payment. - Hanbalis: The Hajj is valid on behalf of the one who commissioned it, because he commanded both. However, he erred by commissioning the Ihram for Hajj from Makkah, while the person entered Ihram from the Miqat. Al-Qadi, from the Hanbalis, held that he should return half of the expenses.