A person by mistake (not knowing the halacha) took old straps (ratzuos) from his Rashi Tefillin and used them on his new Rabbeinu Tam Tefillin (seemingly he got new straps for his Rashi Tefillin.) Sometime later he told over what he had done to a Rov who informed him that he shouldn't have done this. However the question is now, what should be done?
Should he, 1) Leave the straps where they are on the Rabbeinu Tam Tefillin 2) Put them back on the original Rashi Tefillin that he had them on to begin with 3) Take them off and put them in geniza
I'll raise a few points (unorganized) for why some of the reasons would be better over the others. Number 3 is the easy eitzah since it removes all problems. However there is a Taz in OC Siman 154 that says if one can't be "raise up" a certain object to a higher kedusha he should use it for what he can, rather than put it in genizah. Therefore that could be the reason for number 1. Or as well because he was already "m'kadesh" the ratzuos to the R"T tefillin and shouldn't move them now to Rashi -- according to those (al pi kabballah) that one shouldn't change from Rabbeinu Tam to Rashi (and perhaps no reason to put them in genizah then as well.) The reason to put them back on Rashi is to raise them in kedusha and put them back in their proper place (since really the "hekdesh" was b'to'es - done as a mistake.)
These are just some thoughts and possibilities to consider. I'm looking for a clear proof in halacha for one way or another. And of course what any poskim said about such a question.
(BTW the Rov involved in the story told him to do the 3rd option with a twist. He decided he would use the ratzuos for a pair of tefillin that he was putting together for an older bal teshuva getting his first pair of tefillin. However his proof or reasoning I unfortunately didn't hear, that's why I'm bringing the question here now.)