Taqsir or Halq
Taqsīr (التَقصير) is one the obligations of hajj and 'umra. Taqsir involves cutting some strands of the hair from head, beard, mustache, or alternatively one may cut a nail of hand or foot. It is the fifth obligation of 'umra. In 'umra al-tamattu' it is obligatory for a person to perform taqsir (he is not permitted to perform halq) after finishing sa'y.
Taqsir, like other rituals is an act of worship in 'umra. So, it is obligatory that one should make the right intention.
Halq (shaving head) is not permissible, nor sufficient to exit the state of ihram in 'umra al-tamattu'. One must perform taqsir so as to complete 'umra al-tamattu' and exit the state of ihram. If a person shaves his head purposely and knowingly before or after taqsir he/she must slaughter a sheep as kaffara. But, if he has entered ihram for al-'umra al-mufrada, he can choose between shaving head and doing taqsir.
Plucking hair is not sufficient to exit ihram of 'umra al-tamattu'; one should perform taqsir as mentioned. If he plucks his hair instead of taqsir deliberately and knowingly, it is not sufficient. Moreover, he has to pay kaffara for it. If a person plucks his hair instead of doing taqsir unknowingly and then performs hajj al-tamattu', his 'umra is void and the performed hajj will be considered as hajj al-ifrad. If hajj was obligatory for him, on the basis of obligatory caution, he should perform al-'umra al-mufrada after performing the rites of hajj and the next year, he has to perform 'umra al-tamattu' and hajj al-tamattu'. The same ruling applies to a person who has shaved his head instead of taqsir and then performed hajj unknowingly.
It is not obligatory to do taqsir directly after performing sa'y. If a person does not perform the act of taqsir deliberately or ignorantly and without it he wears ihram for hajj, his 'umra would be void and his hajj would be considered as hajj al-ifrad. On the basis of obligatory caution, he should perform 'umra al-mufrada after performing hajj and if his hajj was obligatory, he should perform 'umra and hajj the next year. If a person neglects taqsir inadvertently and wears ihram for hajj, his ihram would be valid as well as his 'umra and hajj, and kaffara is not obligatory for him. However, it is mustahabb to slaughter a sheep or goat as kaffara. Rather, it is a caution not to neglect paying kaffara.
After performing taqsir and exiting the state of ihram of 'umra al-tamattu', every forbidden thing in state of ihram becomes halal including intercourse with one's spouse.