It depends on what your ethical framework is. I'm a consequentialist, so whichever action produces better consequences I think is the right action regardless of the rules. You sound like a deontologist, to whom following the rules (not necessarily the law) is what it means to be ethical.
It's more that I make a distinction between justice and ethics. Ethics is the philosophy of how rules should be made. Justice is sort of a meta-rule, mandated by the most popular ethical systems (utilitarianism, Rawlsian ethics, among a few others). Justice mandates that neither a rule nor its application unduly advantage any party over any other. Therefore, there should not be a rule that prohibits people with a particular skin pigmentation from using a particular seat on a bus. Likewise, enforcement of rules that prohibit actions that victimize others should not be suspended when local law enforcement doesn't like the victim.
I suspect I don't need to explain why it's difficult to get such equitable enforcement without consistency.
If justice is just a meta-rule which says that all rules in an ethical framework should be followed then the only rule in consequentialism is: "do whatever leads to the best outcome." Doing whatever leads to the best outcome can involve breaking laws or applying other rules only at certain times and to certain people. As long as you are acting to produce the best consequences you are acting justly.
This is precisely where our definitions of justice differ. I think something can be beneficial without being just, and vice versa. Justice is just sort of beneficial overall, so we shouldn't violate it without having a really good reason. This "really good reason" thing is what executive pardons (and similar powers) are for, and even that is abused pretty heavily.
Justice does not mandate that all rules be followed. It mandates that all rules be equitable, and be enforced equitably.
Finally, while using the rule "Do whatever leads to the best outcome" is a perfectly good way to operate as an individual, it is unenforceable on a societal level. This is why we have other rules. It's impossible to figure out just what has the best consequences, so we try to produce more concrete rules that improve consequences overall (hopefully which don't have too many consequences of their own).
Following the personal rule "Do whatever leads to the best outcome", even when it goes against society's laws, is called civil disobedience. When done for a good cause, it is not generally vilified. The catch to civil disobedience is that you must accept the consequences of your actions.
You aren't considering the externality of blowing the whistle on bad contracts by leaking confidential information: that you are setting the stage for other people to exercise their judgement poorly as well with information that is much more hazardous to leak.
