If a user modifies or changes their username it is up to them.
–as long as the username is not offensive and does not slander anyone–
The same principle applies to a candidate regardless if that change occurs during a moderator election.
It is very dangerous if a candidate changes their name during elections to support what they were previously against about.
First of all, the candidate did not change their username, they added a tagline. As long as a candidate remains identifiable, tagging a slogan shouldn't make any difference and there is nothing “dangerous“ about it. Moreover, completely changing a username during an election is counterproductive, a candidate wants to be recognised.
The OP's blatant mistrust of the candidate may or may not be warranted but one thing is clear though, that ‘political’ statement during the election period has backfired on the candidate. If they want to shoot themselves in the foot, let them do so. Even the simple act of changing or modifying a username during an election provides significant insight into the candidate's personality and/or their stance on a position.
Consider this: SE decides to roll back the recently modified username, and… cue uproar from community. Accusations of censorship, blocking free speech, double standard, questions on whether it violates CoC etc. etc.
The Community Managers and moderators on Stack Overflow did absolutely fine not to intervene. Sometimes it pays to step back and allow nature to take its course.
UPDATE
I checked the election page, and noticed that the candidate's username no longer carries the familiar slogan of last year. I have no idea how, when, or who instigated this change.
Response:
The name was changed back by the user themselves. No moderators or staff were involved @Cody Gray
2nd UPDATE
The candidate's request to delete their account on Stack Exchange has been granted.