The "painful quirks" can be overcome, yes. But I doubt they are much like a leopard changing it's spots. More like, camouflaging them. For instance training yourself to make eye contact isn't the same as removing the inability to maintain regular eye contact. it is merely consciously deciding to control your eyes. I have never had too much trouble with eye contact... my problem is more the drill like stare.... so please, correct me if I am wrong.
As for emotions that go along with it... emotions themselves can not be controlled. They are the subconscious reaction to our values. A lightning calculator of our pre-conceptual judgment of any given situation. If you believe you are somehow deficient for not being able to make eye contact, your emotions will respond in kind by making your "feel" guilty, or sad, or angry, or hurt etc... As such they are very changeable. I used to beat myself up all the time about being unable to change my routine, or for my lack of friends. Or for any number of things I thought I should have been able to do, but could not.
So you will most likely find that if you employed introspection you would discover the thought patterns and value system behind those emotions. And thoughts can be changed. And as they change and become automated... the emotional response will change to suit. So, at least in that respect, a leapord can change it's spots. Or, more accurately, they can change how they view there spots.... with either acceptance or shame, joy or disgust, etc...
As far as changing the ACTUAL spots themselves.. no, I don't believe they will ever change. Only the opinion of those spots. The spots might fade with age, or change shape slightly, but they'll be there, always.
Apart from that.. yes I can relate.