I have done several AYAW demo's and have also used it as a great party game.
The only character I have added has been a character I call the wizard.
But there are very specific conditions for this.
There must either be less then 7 players.
This holds true for each set of 15 as well, if there are 16 to 22 players.
Less then enough for a stand alone village.
Game play follows as normal.
During the night phase, just before dawn, (after the werewolves and seer) the magician can choose one person to protect.
That person may be themselves if they so choose.
If the magician is lucky, he/she will save at least one or two people.
This extends the game play for one or two turns.
As far as allowing people more variety:
Before any cards are passed out, I encourage each player to come up with a unique character/persona for themselves. (Note: I said encourage, not force or require) this usually quells any "boredom" with being a villager again.
I also hand out the AYAW etiquette cards to any new players (or old players for that matter) to help get them in the spirit of the game.
I do have a use for AYAW blanks though. (I LOVE blanks)
Use them in conjunction with the standard cards as character cards. That way no one feels pressure to come up with a persona.
Hand out a sheriff card, a mayor card, beauty queen, etc...