Q. If one replaces a mezuza with a better one, does he have to say a brocho? What happens if he already had in his possession this new better mezuza for months and at the time the present mezuza to be replaced was attached?
A. Sefer Hoeshkol (H. Mezuza p. 73b) maintains that a new brocho is needed if a different mezuza was placed. This applies even when done immediately after taking down the old one (Ikrei Dinim 30: 6 quoting Pachad Yitzchok, or when one already had in his possession this new better mezuza at the time the present mezuza to be replaced, was originally attached.
Horav Shlomo Miller’s Shlit’a opinion is similar. The Rov added that one should use the mezuza removed in another location. If it is not needed at all, he should donate it to one that needs a mezuza and can’t afford one.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a