Maybe... but probably not.

I wouldn't THINK that cutie marks can ever change...but it's possible. I've wondered about this exact same thing! What if later in life you discover another talent, skill, purpose, passion, interest, etc., that impacts your life even more than what your cutie mark represents? I figure that the marks are usually general enough and can be interpreted in enough different ways that the essential parts of you they symbolize will always be relevant, though...

It's a good thought, but I doubt it. If you think about it, each pony has more talents than their cutie marks show. (For example, AJ and Pinkie can bake.) Plus, Equestria is such a wonderful place, there would be no mid-life crises. I feel like everypony is really able to pursue their dreams and live life to the fullest. So their special talent always sticks with them, and they can always succeed if they try hard. (Ugh, that sounds so sappy...)
Anyway, there's nothing in the show that would indicate that, so I have no reason to believe that it could be the case. I'm a grumpy, strict, canon-only person.

Well, I really doubt their cutie marks can change. For example, Princess Celestia and Princess Luna are both princesses right? So, they could've had a crown/tiara or a throne as their cutie mark. But they got the sun and the moon.

if they had 2 cutie marks that would be awsome

Indeed

That sounds like an interesting theory but I have to agree with BillyTheShark's comment to disagree with the theory

That would screw everything up!

Comepletely impossible...this just reminded me of Magical Mystery Cure,it will end up like that...besides your cutiemarks dont change,its like Twilight,her talent is magic in general thats why she has that cutiemark but she's also a bookworm,she has gained a lot of knowledge and lives in a library too,did her cutiemark change? no,its her special talent its possible that you are good at more than 1 thing :)

I doubt it. How can your talent change just because something bad happens to you emotionally?