"Pandora! That wasn't very Fabian!"
"Hannibal for life."
Because of course she'd want that
Pandora actually pushing for the change herself was a relatively late addition, but given her son?
Yes. Regardless of whether it was what her enemy wanted, she was going to try for it.
And predictably, it did NOT go well.
Ragnarok
There are plenty of in-universe reasons that immortal chose the name Ragnarok from Norse mythology.
Out-of-universe, however, there is another reason:
That's what younger me called a really powerful "final boss" dragon they made up.
(Don't read too much into it being a "final boss". Or do, if you like things being excessively ominous.)