From: Rabbi Moshe Sofer
To: Rabbi Berl
The Chasam Sofer rules that one may not inflict a blemish on a safek bechor even according to those who hold the prohibition is merely Rabbinic in our time, because such an act constitutes the very appearance of blemishing kodashim, and the safek bechor already carries Torah-level restrictions of shearing and work. He further defends the Rambam's position that the prohibition remains Torah-level, grounding it in R. Yochanan's interpretation of the word "kol" as a genuine Torah-level inclusion extending the ban to our time.
Source: Shu"t Chasam Sofer YD §306