Is it permissible to fast one day of an oath's expiation (kaffarat al-yamin) one or two days before Ramadan, knowing that it is not permissible to join (consecutively fast) it with the fasting of Ramadan?

It is not permissible to switch to fasting for the expiation of an oath except after the inability to feed or clothe [the poor]. It is permissible to fast the end of Sha'ban for expiation, as the prohibition of fasting the end of Sha'ban relates to the intention of observing caution for Ramadan. If you possess wealth, then expiate by feeding or clothing; otherwise, fast. If Ramadan begins, then fast the remaining days of the expiation after it ends. You are not obliged to pay expiation for delaying the disbursement of the expiation, but you are obliged to repent and seek forgiveness if the delay was without a valid excuse.