Isn't intercession a follow-up and alteration to Allah's decree after He has ordained it, in light of His saying: "And Allah judges; there is no one to overturn His judgment," and "The Word with Me will not be changed, nor am I in the least unjust to the slaves"?

The established intercession (shafa'ah) does not contradict Allah's decree (qada') and preordainment (qadar), because it only occurs with Allah's permission and contentment, as stated in the verses: "Who is it that can intercede with Him except by His permission?" (2:255), "On that Day no intercession will avail except for those to whom the Most Merciful has granted permission and whose word He has approved." (20:109), "and they do not intercede except for whom He approves." (21:28), and "And intercession will not avail with Him except for one to whom He gives permission." (34:23). Intercession is an implementation of Allah's judgment, an act of mercy for the one interceded for, and a manifestation of the intercessor's honor. There is no contradiction between the negation of intercession in the Qur'an except by Allah's permission, and its affirmation.