Depends on your definition of unstable. If by unstable you mean genetically unstable; like say a truely HA dog...then no I don't think you can create that kind of instability. However if you mean behaviorally unstable...then yes, absolutely I agree, environment and experience can influence behavior and undesirable, unstable, dysfunctional behaviors can be learned. The difference for me is that learned behaviors can (if someone is inclined to put in the time and dedication) be unlearned or at least modified through training, counter-conditioning, desensitization yadda yadda...whereas genetic instability is simply physiological...maybe it can be medicated...but it will always be there.