Noto una recente tendenza della stampa satirica a terminare in 'y' alcuni cognomi; per esempio, oggi leggevo Renzy per Renzi e Alfy per Alfano.
Sapreste dire quale sia l'origine di questa modificazione, e se la stessa è usata anche in altre lingue neolatine?
I believe we can agree that this specific use in the Italian press is an attempt to sound "English" (many think it is "cool", "modern" - Italians are known to be xenophilous after all), hence we should call it an "anglicism".
Specifically it is a diminutive form of a given name (this is called a "hypocorism") and is typically used as a "term of endearment" ("vezzeggiativo", in Italian). Of course, such diminutive terms of endearment can also be used sarcastically as derogatory terms, as in the examples mentioned in the question.
I ignore the origin of the suffix "-y" as a diminutive (a "hypocorism by reduction"), some say it is of German origin, egreg suggested in his comment above it is of French origin. I suspect it might be common to more than one language.
Some reading (links from english.stackexchange):
On the origin of the English diminutive suffix -y, -ie, The Free Library
Etimology of suffix -y, Wiktionary
In questo specifico caso, Renzy puo' essere semplicemente la storpiatura di Renzie (a sua volta derivato da un'analogia fatta fra Renzi e il personaggio Fonzie). Questo l'ho trovato soprattutto nei commenti degli utenti, non tanto nei titoli della stampa.
