Is a man's shaving of his head with a "number 1" before 'Umrah, then removing the rest with a razor after the circumambulation (tawaf) and the ritual of walking between Safa and Marwah (sa'i), considered valid for his release from the state of ihram?

What the man did by shaving his head before 'Umrah is permissible, and his 'Umrah is valid. The state of ihram was exited by his final shaving. There is no harm in shaving the hair before going for 'Umrah. In fact, some scholars have held that it is commendable to do so, so that the person in ihram may be relieved from the discomfort of hair.