May components (batim, straps, parashiyot) from a Rashi tefillin set be exchanged with components from a Rabbeinu Tam set after they have been worn?
Synopsis
Once a pair of tefillin has been worn for the mitzvah, its components become consecrated to that arrangement (Rashi or RT), and exchanging components between the two sets is forbidden. The Pri Megadim and later authorities rule that even a prior condition (tenai) to enable future exchange does not help once the tefillin are used.
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Discussion
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