Changing something like this would definitely require a reapp, yes. Deciding to change a character from an elf into a dragon would also change their backstory and, in in many cases, parts of their personality.

For a change as big as this, I would suggest dropping your current character, waiting for the new character's approval, and then playing that new character as if they were truly new to the game. Otherwise it may confuse other players and characters as to why your character is suddenly different with no in-game explanation.