Am I obligated to offer expiation after changing my intention for Hajj from Qiran to Ifrad, to be consistent with my companions, knowing that I intended 'Umrah several times thereafter?

If the intention is changed from performing Hajj and Umrah together (Qiran) to performing Hajj only, and this change occurs before entering into the state of Ihram, then there is no obligation upon you. However, if this change occurs after entering into the state of Ihram for both Hajj and Umrah, then the ruling of Qiran (combining Hajj and Umrah) is not lifted from you. The acts of your Umrah will be included in the acts of your Hajj, and you will be required to offer the sacrifice of Tamattu'.