When Removing Mezuzos for Checking the old nails, screws and tape previously used to affix the Mezuzos may be discarded. However, Mezuzah cases and Mezuzah wrappings if no longer needed should be treated as sacred material and require genizah/interment, after their use.
It is preferred to have all of the mezuzahs returned to their original doorposts, or at least to the same type of entrance way (i.e., from one bedroom door to another, or from one archway to another) in order that you don’t lower the status of a Mezuzah that was once on a door required Midoraisa (Biblical) to a entrance way that is only Rabbinical.
A practical suggestion: when removing the mezuzahs, label each mezuzah case with a number (using masking tape or the like). Tape an identical number on the doorpost from which it was removed. When the mezuzahs are remounted, match the numbers from your cases to the numbers on the doorposts.
When removing Mezuzos for Checking, or renovations are being done, or for any other reason when the Mezuzah is remounted, the blessing should be recited only if the Mezuzah was off the doorposts for at least one night. If you are also adding new Mezuzahs at this time, it is preferable to recite the blessing on a new one (providing that it is mounted on a door that requires a blessing).
The Sofer Center Sofer Stam in Monsey NY 10952 845-262-0246
Rabbi Kass was ordained by Rabbi Yisrael Meir Lau, former Ashkenazik Chief Rabbi of Israel. He is certified as a Sofer for both Kesivah and Hagoah by one of the leading experts in Safrus, Rabbi Avrohom Tzvi Vosner, Rav of the Vad Mishmeres Sta”m.