Let me give you historical examples where this was done, and how/when this has been done well in popular fiction.
Starting in fuedal Japan, the height of the 'samurai age' there. When a boy is born, he's given a name. Literally referred to as his 'childhood name'. As he studies the way of the samurai (Bushido, lit. the way of the warrior) and grows in his training, he is eventually granted the title of samurai. To symbolize this, he takes a new name.
Then how about 'Christian names'. In many places across the Christianised world, you have a 'cultural name', if you country was recently Christianised, or more predominantly in African countries. But when you are baptised, you take a 'Christian name'. FYI, this is still a common occurrence in the Netherlands, where if you live in the 'bible belt', people will tell you their 'Christian name' is [...].
This is also quite common in Western Pop Culture. See P. Diddy (or was it Puff Daddy...?) The Edge, The King of Rock and Roll. It's common for someone to 'take a new name' as a performing artist, or a writing pseudonym.
Now, onto fiction. The Elder Scrolls V: Skyrim. The first emperor of Skyrim was known by many names. Talos of Atmora, Tiber Septum (birth name, btw), the Hero-god of man, the God of War. If you refer to any of these names, you refer to Talos, and likely to Talos worship which is outlawed by the White Gold Concordat. It's not wrong to refer to this person by any of these names, even though the name used to refer to him does show what you wish to see in him (like the OP suggests for the name change in the phrasing I answer).
Another, and perhaps even more famous example, is Count Dracula. In the original work of Bram Stoker, he isn't referred to by much other than his name or station, but. Look at how modern fiction portrays this iconic character. From Hellsing and Hellsing Ultimate (Alucard, lit. name spelled backwards). To Vlad the Impaler (historical basis). To the Scourge of the Turks (historical basis). To the Father of the Vampiric Nation, and Drake (Blade Trilogy). In many vampire mythos, Dracula is the Adam of the vampires, the progenitor and has either a cult-like following, or a mythic status, or a god-like presence in which nations fall when he rises in the night.
Another common trope used in mystery novels, and sometimes thrillers, is an almost 'split personality' type villain, where (s)he's in plain sight the whole time, but secretly plotting behind your back or acting via proxies and often under a pseudonym. In this way, how the narrator refers to the villain is decided purely on whether they are 'villaining' or 'hiding'.
So. I'd have to say, if the narrator changes the name being used, there is precedent in history, fiction, and pop culture. So go for it.