In Shearim Metuzyanim Behalacha, Chap 122, 5), Rav Braun z"l states that
someone who normally shaves two or three times a week is allowed to shave
'lechavod Shabbos' (in honor of the Sabbath). He bases it upon responsa of
the Chasam Sofer, and inferred from the Magen Avraham.