It might not be anyone's business but the Turks', but I am very curious. What prompted the name change to "Istanbul"? Especially since the city had already been under Turkish rule for quite some time before the name was changed, and since controlling a great city of antiquity is a pretty big feather in your fez.
Like New York, Constantinople had a lot of nicknames in several languages. One of these was simple "The City." In Turkish this is transliterated as Istanbul. The earliest attestation of it being called Istanbul comes from the 10th century. So the nickname predates Turkish conquests by centuries. The more formal and proper name in Turkish was Kostantiniyye, replacing the Greek place name -polis with a Turkish equivalent.
Both Kostantiniyye and Istanbul existed side by side for centuries. After the Ottoman conquests, both names were used officially. For example there were still coins stamped Kostantiniyye in the late 19th century. But there were officials that had Istanbul as part of their official titles.
In 1923 when the Turkish Republic was declared there were a lot of efforts to remove old Greek influences. So the government declared Istanbul to be the official name. They requested that all other governments refer to it as Istanbul exclusively and they stopped delivering mail that used alternative names. So it became Istanbul exclusively pretty quickly.
As a follow up, I believe the song the title refers to was a follow up or mocking a previous song insisting Istanbul should be called Constantinople. Is that right? If so, what was the song.
Hi, you may be interested in this explanation from /u/borafan
When Mehmet II captured the city in 1453, he did mull over a number of name changes. Istanbul was a term that was alive and well at the time and he considered renaming the city. At one point he even considered naming it Islambol ("Full of Islam") as a pun on Istanbul. Ultimately, however, he decided he didn't want to keep the traditional name (it was Konstantinopolis to the Greeks; this was sometimes truncated to Stanpolis by the Turks), so he modified it slightly it: Kostantiniyye. Which, given the tendency of "iyye" to crop up in Arabic exonyms, was probably just the best way to transliterate it to the Arabic script (Turkish wouldn't adopt the Latin alphabet until the 20th century).