There's nothing scandalous about it -- that's rather a hyperbole and shows very little understanding of the term scandal -- but just the typical excessively legalist view of the law. In Eastern Europe, it's LONG been the custom to add an interjection in between the "fruit of thy womb, Jesus" ... and the "Holy Mary, Mother of God", briefly calling to mind something about the mystery, i.e. "... blessed is the fruit of thy womb, Jesus ... Who rose from the dead on the third day ... Holy Mary, Mother of God, pray for us sinners ..."
Certainly if you add something to the Rosary that SUBSTANTIALLY changes it into something other than the Rosary, then the indulgences for the Rosary would not apply (e.g. like some people who use it to offer some other type of "chaplet" prayer), but adding such interjections does not substantially change the Rosary from being the Rosary.
Too much legalism. It was the same nonsense Fr. Cekada tried to apply when eliminating the Prayers after Low Mass ... though he was wrong even from the legal standpoint.
If adding something to the Rosary eliminates the indulgence, without adding the distinction that it must substantially alter the Rosary, then if you stutter and add an extra word at any point, or repeat a word, of even accidentally skip a single word, then you haven't prayed the Rosary? That's just nonsense. And talk about this causing massive angst among the scrupulous, who now might be seen restarting the Rosary the second they accidentally add or omit something. At that point, you're just better off forgetting about the indulgences and just praying the Rosary out of love for God, Our Lord, and Our Lady -- with the alternative being the development of mental problems and neuroses. Pray the Rosary because Our Lady asked us to and gave us her own personal "indulgence" by talking about how she'll endow it with great power to solve any problem and turn it into a weapon against evil. This smacks of Pharisaism here and extraordinary scrupulosity.
Almost everything either in the Magisterium entails the qualifier of "substantially". When the Popes have taught that there can be and has never been error in the Magisterium, they mean SUBSTANTIALLY and not absolutely. When Sacred Scripture says that all have sinned except Our Lord, they mean generally but not absolutely (to the exclusion of Our Lady as the Prots would have it). Similarly, any wording around indulgences undoubtedly means that if you add something that SUBSTANTIALLY alters the Rosary into no longer being the Rosary, then obviously the indulgences for the Rosary would not apply, since it's no longer the Rosary ... not some nonsense where if you take it with his meaning, the accidental addition of a single word would cancel the indulgence. When you announce the next mystery between decades, moreover, is there a "standard"/"approved" verbiage for those where if you add a single word, that too cancels the indulgence. So if the typical mystery is "the Assumption of Our Lady" and you say "the Assumption of Our Lady into Heaven", does that cancel the indulgence because you added "into Heaven"?
