Is it sunnah to adhere to the supplication "O Allah, guide me among those whom You have guided..." in the Qunūt of the Fajr prayer, and is it permissible to supplicate for the destruction of the enemies of Islam and the salvation of the oppressed instead of it, or by combining the two?

The qunut in the Fajr prayer is a matter of scholarly disagreement. If one holds the view that it is legislated, then it is preferable to adhere to the transmitted supplication. It is permissible to supplicate for the destruction of the enemies of Islam and Muslims and for the salvation of the oppressed, or to combine the transmitted supplication with other supplications. The matter is broad in this regard. The preponderant view is that the qunut does not require a specific wording.