It is not permissible to replace stoning of an adulterer with killing by the sword or by shooting
Question

                Is it permissible to execute a married adulterer by some method other than stoning, such as killing him with a sword or by shooting him?.
Praise be to Allah.
    It is essential to stone the married adulterer until he dies, 
    following the Sunnah of the Messenger  (peace and blessings of Allaah be 
    upon him), as it is proven that he said that, did it and enjoined it. The 
    Messenger of Allaah  (peace and blessings of Allaah be upon him) stoned 
    Maa’iz, the Juhani woman, the Ghaamidi woman, and the two Jews. All of that 
    is proven in saheeh ahaadeeth narrated from the Prophet  (peace and 
    blessings of Allaah be upon him). The scholars among the Sahaabah (may 
    Allaah be pleased with them), the Taabi’een and those who came after them 
    are also unanimously agreed on that. No one differed from them apart from 
    those to whose views no attention is to be paid. Al-Bukhaari and Muslim 
    narrated in their Saheehs from Ibn ‘Abbaas (may Allaah be pleased 
    with him) that ‘Umar (may Allaah be pleased with him) said: “Allaah sent 
    Muhammad  (peace and blessings of Allaah be upon him) with the truth and 
    revealed to him the Book, and one of the things that Allaah revealed was the 
    verse of stoning. We have read it and understood it. The Messenger of Allaah 
     (peace and blessings of Allaah be upon him) stoned (adulterers) and we 
    stoned (them) after him, but I fear that there may come a time when some 
    people say: ‘By Allaah, we do not find the verse of stoning in the Book of 
    Allaah.’ So they will go astray by forsaking an obligation that Allaah has 
    revealed. According to the Book of Allaah, stoning is deserved by the one 
    who commits zina, if he is married, men and women alike, if proof is 
    established or the woman becomes pregnant or they confess…” 
Based on this, it is not 
    permissible to replace stoning with killing by the sword or shooting, 
    because stoning is a more severe punishment and a more effective deterrent 
    to the sin of zina, which is the most grave sin after shirk and killing a 
    soul whom Allaah has forbidden us to kill. The hadd punishment of stoning 
    for a married person who commits zina is one of the matters that is 
    determined by the Qur’aan and Sunnah and there is no room for ijtihaad or 
    personal opinion. If killing by the sword or shooting were permissible in 
    the case of the married adulterer then the Prophet  (peace and blessings 
    of Allaah be upon him) would have done that and would have explained it to 
    his ummah, and his companions after him would have done that too.