Is it possible to change a vow to memorize Surat Al-Baqarah and Surat Al-Imran to something else, for fear of not being able to fulfill it, knowing that the time for fulfilling the vow has not yet come?

A vow to memorize Surahs Al-Baqarah and Al-Imran is a vow of obedience that must be fulfilled, whether it is absolute or contingent upon the fulfillment of a condition. It is not permissible to change it to another act of obedience, even with incapacity or certainty of it. If incapacity actually occurs, an expiation for breaking an oath (kaffarat yamin) becomes obligatory, based on the Prophet's (peace and blessings be upon him) saying: "Whoever makes a vow and is unable to fulfill it, its expiation is the expiation for an oath."