As a rule, an object which was designated for a higher level of kedusha may not be used for a matter of lower sanctity. An item that was used for a lower level, however, may be repurposed for a higher level. Therefore, anything which was used as a part of the shel rosh cannot be used for the shel yad. Even in a case where an item can no longer serve the higher purpose, it should not be used for the lower matter. Instead, it should be put into genizah (burial).
סעיף א, ס"ק ג, וביה"ל ד"ה אסור וד"ה מהם