Is it permissible for the one offering the sacrifice (Al-Udhiyah) to trim their nails or cut their hair before the time of the sacrifice if they are unable to refrain from doing so?

The sacrificer must refrain from cutting his nails and shaving his hair until he slaughters his sacrifice, due to the Prophet's (peace be upon him) saying: "When you see the new moon of Dhul-Hijjah, and one of you intends to offer a sacrifice, then let him refrain from [cutting] his hair and nails." If he does any of that, he must seek forgiveness, and there is no expiation upon him, especially if he was in need of doing so. Some scholars merely disliked that. The sacrificer should cut his nails and remove hair before the beginning of Dhul-Hijjah.