If an Ashkenazi specifically has in mind when putting on his tzizis that if he should remove them even for a short period of time (a shower), it should be considered an hesesech hada’as: Would this be halachcaly correct thus requiring a new beracha? Is there a problem with such a practice? Does it matter when this intent takes place, either after putting tzizis on or when the tzizis are removed?
Answer:
A similar idea is mentioned by the Mishnah Berurah, and because many rishonim side with the ruling of the Shulchan Aruch (whereby a person can make a new berachah after taking off tzitzis even for a short time), one may rely on it for making a berachah.
One needs to have intention at the time of the berachah that the berachah should only last until the time that you take off the tzitzis.
Sources:
The Magen Avraham (639:17) writes explicitly that a person cannot limit the blessing on tzitzis for a given period of time. He gives this as an example, and writes that the same applies to the blessing on sitting in a Succah, which cannot be limited for one meal alone.
However, the Chacham Tzvi (22) writes, with regard to Birkas Ha-Torah, that a person can limit the application of his berachos.
A similar dispute is found in the Tevu’os Shor (19:17), concerning the berachah over Shechitah. Although Peri Chadash writes that one can limit his blessing (and gives this as advice for getting out of a safek), Tevu’os Shor contends that this cannot be done.
The Chayei Adam (49:11) implies that it is possible to limit one’s berachos (with regard to berachos on foods), and this is also implied by the Shulchan Aruch itself (174:4), concerning limiting the berachah on wine. However, it would appear that this limitation applies specifically to distinct acts (such as eating something new), and not to tzitzis, which is just one continual act of wearing the tzitzis. This distinction emerges from the glosses of Chasam Sofer (on the Magen Avraham).
Based on this distinction, we can understand the ruling of Rabbi Akiva Eiger (25:5), who writes that one can limit the blessing on tefillin, and the ruling of the Mishnah Berurah (Biur Halachah 8:14) concerning tzitzis: It is possible to limit the blessing that it should not apply to the new act of wearing tzitzis that a person does after taking off the tzitzis (even for a short time).
