What I'm really enjoying is having post topics being driven by questions I'm asked at auditions or by e-mail. The question of who you are as a voice type being set in stone is an interesting one, and certainly a question that has implications for auditions.
To give a quick (and probably predictable) response to this topic heading: it depends.
If you look at any number of operas, you will see that there is a colorful history of different types of voices singing various roles.
Examples (with some well known singers):
Don Giovanni: Bass: Samuel Ramey, Baritone: Thomas Allen
Leonore in Fidelio: Soprano: Karita Mattila, mezzo Christa Ludwig
Figaro (in Marriage): Bass Baritone: Jose Van Dam, baritone: (again) Thomas Allen
Susanna (in Marriage): Soprano (take your pick) Mezzo: Cecilia Bartoli
Anyway, you get the idea - and this doesn't even cover the different weights of voices within these categories doing some of the same roles.
In any case, the dilemma is - how much of a limb can you go out on at an audition? If I'm a soprano, will anyone want to hear me do Rosina? If I'm a lyric baritone with solid low notes, is Se vuol ballare ok? You get the picture.
So, what should you do? My opinion on this is that the less established you are, the smarter it is to stay "between the lines". As you become more established, people who hire you are going to be more willing to take a "not obvious" chance with rep when it comes to you (they may even wind up using this as a marketing hook). As with anything I am saying here, there are exceptions.
I will say more about this in another post, but feel free to weigh in on this.