Date: Erev Rosh Chodesh Elul 5573
From: Rabbi Moshe Sofer
To: Rabbi Tzvi Avigdor
The Chasam Sofer resolves the Pri Megadim's difficulty with Tosfos in Nazir 57b by arguing that the Torah's command for the metzora to shave contemplates cases where only an obligated Jewish man is available, thus proving a positive commandment overrides even an active negative commandment. He further argues that the nikaf always violates the prohibition even without assisting, so using an exempt person does not constitute fulfilling both commandments simultaneously.
Source: Shu"t Chasam Sofer YD §141