The ruling on changing the ihram intention depends on the direction of the change. Adding Hajj to an existing Umrah intention (converting from ifrad Umrah to qiran — combining Hajj and Umrah) is permissible according to the majority of scholars, provided this is done before beginning the tawaf of Umrah. Once tawaf has begun, the rites of Umrah have started and the intention cannot be changed according to most scholars. Sheikh Ibn Baz confirmed this ruling, noting that the Prophet (peace be upon him) himself performed qiran, combining Hajj and Umrah in a single ihram.
The more debated question is whether a pilgrim who entered ihram for Hajj alone (ifrad) can change their intention to Umrah (converting to tamattu). This is based on the famous incident during the Farewell Hajj when the Prophet instructed his companions who had entered ihram for Hajj but did not have a sacrificial animal (hady) to change their intention to Umrah, perform tawaf and sa'i, cut their hair, and exit ihram, then re-enter ihram for Hajj on the 8th of Dhul-Hijjah. Sheikh Ibn Uthaymeen held that this option remains available to pilgrims today, not limited to the companions alone.
The Permanent Committee ruled that a pilgrim may change from Hajj to Umrah (becoming mutamatti') as long as they have not begun the rites of Hajj. However, the Hanafi and Maliki schools generally do not permit downgrading from Hajj to Umrah once ihram for Hajj has been assumed. If a pilgrim is unsure of their intention, they may make a conditional intention (ishtirat) at the time of entering ihram, saying: 'If something prevents me, my place of exit from ihram is wherever I am stopped.'