Question: We moved into a rented flat and removed the mezuzos to get them checked and put them back up the same day. They were all kosher. Should we have said a new beracha?
Answer: The Shulchan Aruch (OC 8:14) writes that if one removed their tallis, they recite a new beracha when putting it back on, even if they intended on doing so when they removed it. The Rema disagrees, writing that if one had the intention to put it back on, one does not recite a new beracha when they do so.
The Aruch Hashulchan (YD 289:4) compares removing mezuzos to be checked, to a tallis. If one replaces them the same day, one would not recite a new beracha. Only if one replaced a non-kosher mezuza with a new one would one need to recite a new beracha.
The Chida (Birkei Yosef YD 286:10) and Kitzur Shulchan Aruch (11:7) write that there is a safek (doubt) as to whether one who removes a mezuza to check it would need to recite a new beracha when reaffixing it. The Pischei Teshuva (YD 289:1) questions why this would be different to removing one’s tallis or tefillin. He suggests that as one removes their mezuzos to be checked, they are not convinced that they will be found kosher and therefore one may need to replace them with other mezuzos. Similarly, R’ Ovadia Yosef (Yabia Omer YD 3:17; Yechave Daas 3:80) maintains that there is a difference between tallis and mezuza and one would recite a new beracha when reaffixing it after having it checked.
However, the Maharam Schik (YD:285) writes that even those who maintain that one would not recite a new beracha would agree that if one affixed a different mezuza, one would do so.
In conclusion, Ashkenazim do not recite a beracha when reaffixing a single mezuza the same day it was removed while many Sefardim do. Even Ashkenazim would recite a new beracha if the mezuzos were replaced entirely and switched around.