When was "Melech Elyon" first truncated, and why?
During Rosh Hashana davening, there's a piyut (liturgical poem) that appears before Untaneh Tokef, that begins "מלך עליון" (Melech Elyon). The commentary by Rabbi Lord Jonathan Sacks, in the Koren Rohr Family Rosh Hashana Machzor, says this:
מלך עליון The Supreme King. A glance at the first letter of each verse shows that this poem has been truncated: the verses beginning with even-numbered letters — bet, dalet, vav etc — have been deleted. Initially each pair of verses contrasted God the sublime King, Melekh elyon, with a human ruler, the destitute king, melekh evyon. Evidently this was considered disrespectful of the rulers of the countries in which Jews lived, and contrary to the principle, "Pray for the welfare of the government, for were it not for fear of it, people would swallow one another alive" (Avot 3:2).
Only the first and last of these verses are usually said, toward the end of the poem. They are said in an undertone with the Ark closed. The poem as a whole has as its theme the central idea of Rosh HaShana itself: that God, Creator of the universe, is its supreme Sovereign. He is King, not only of the Jewish people, but of all humanity, of all that lives.
The piyut is presented in its truncated form in the machzor, with the full version, all of the verses about "melech evyon", available in the back.
Do we have any sources on when it was first truncated, and what the context may have been? It doesn't seem to me like it was a mandatory censorship (such as what the case was with Aleinu), because we still have the full text, and that's not the impression I get from Rabbi Sacks's commentary, so I'm curious if we know when and why that decision was made to omit the majority of those verses.