Translation notes for the Guardian Fan-song 一令長安 / A Writ of Lasting Peace, novel excerpts included as well as credit at the end, do take a look at that — like a lot of great fan productions, it was made by an army of fans.
Link to song profile on music163 (leave comments here)
Link to song profile on 5sing (has fanart)
Art FMV on bilibili
Drama FMV on bilibili

For the novel lines, I made notes, but for the lyrics, I’m putting down my initial ‘meaning’ draft and the full sentences I constructed from them.

一令長安——鎮魂同人曲（劇情版）

A Writ of Lasting Peace - Guardian original fansong (plot version)