There is nothing wrong if the person who has been appointed to slaughter a sacrificial animal cut his hair during the first ten days of Dhul-Hijjah.
Sheikh M. S. Al-Munajjid, a prominent Saudi Muslim lecturer and author, states: it is permissible for the one appointed because the prohibition on cutting the hair and nails only applies to the one who is offering the sacrifice, that is, the owner of the animal. The one who is appointed to do that on his behalf is not obliged to adhere to this.
Also, Sheikh Abdul-`Aziz ibn Baz, the late Mufti of Saudi Arabia, stated: Those who are appointed to do this on the behalf of others are not the ones who are offering the sacrifice; rather, the ones who are offering the sacrifice are the ones who appointed them to do that.