I don't know about international aviation law, but in the U.S. the text is:
91.3 Responsibility and authority of the pilot in command.
(a) The pilot in command of an aircraft is directly responsible for, and is the final authority as to, the operation of that aircraft.
(b) In an in-flight emergency requiring immediate action, the pilot in command may deviate from any rule of this part to the extent required to meet that emergency.
This does not mean pilots can break rules as long as they make sure to do so safely, but if a situation is unsafe they may break all rules necessary to make it safe again. Furthermore, pilots are required to inform ATC of any deviations they made from the regs or ATC instructions (of course this is one of the rules they're allowed to break if making such a radio call would be unsafe). Again, this is only for the U.S., but other countries do tend to look us for how to do aviation safety.