Alexandria of Egypt actually would count.. Perhaps?. While it's true Alexander founded the city. It's also true he built it on top of the existing Egyptian city of Rhacotis.
Alexander the Great both founded cities and renamed existing cities after himself. It is claimed Alexander named 70 cities for himself in total.
From: The Many Alexandrias of Alexander the Great
According to the great biographer/philosopher Plutarch, Alexander founded at least 70 cities, although this number probably include pre-existing settlements renamed and/or repopulated by Alexander.
Alexander also named two cities after his horse Bucephalus and after his dog Perita respectively.
Examples of existing cities which Alexander renamed after himself include:
Also From: The Many Alexandrias of Alexander the Great
- Alexandria, Egypt: Easily the most famous of all Alexandrias and one that remains a major metropolis today of well over 4 million people, Alexandria, Egypt was founded in 331 BC by Alexander to be the new centre of Hellenism in Egypt. The new city was built on the site of the pre-existing city of Rhacotis; within a century, it was the largest city in the world. Despite the various rulers that have come and gone in the ensuring millennia (the Ptolemies, the Romans, the Sassanids, the Ottomans, the British, and the current republic of Egypt), Alexandria has maintained its prominence as the second city of Egypt behind Cairo.
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- Alexandria by the Latmus: This is likely the ancient fortress city of Alinda in the modern-day Aydın Province of Turkey which dated back many hundreds of years before Alexander. Apparently refounded as a military settlement in 333 BC, the city was returned to its previous name sometime before 81 BC. Coins were still being minted here into the 3rd century AD. It, too, remains a titular Catholic see, although no bishop has held the title since 1976.
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- Alexandria Arachosia: This is Kandahar, the second-largest city in Afghanistan. Prior to Alexander’s arrival at the end of 330BC, this was likely the Achaemenid city of Kapisakaniš. Arachosiawas another satrap roughly equivalent to today’s Kandahar and Helmand provinces. The name ‘Kandahar’ itself derives from ‘Alexandria’ (Iskandariya). Despite its location near the edge of the empire, the city remained culturally Greek for some time after Alexander’s death. Today, Kandahar is known primarily as one of the major battlegrounds of the War in Afghanistan.
For a more complete list see the source given above.