When it comes to expressing defiance or disobedience in a formal way, "in contravention of something" would be a reliable phrase to use. Nevertheless, there are various alternative synonyms to incorporate if you're looking for a change of style. Some commonly used expressions to convey the same meaning include "in violation of," "against," "contrary to," "despite," "in defiance of," "in opposition to," and "disobeying". These phrases give a similar sense of rebellion or noncompliance, and can be used interchangeably in most instances. Choosing the most appropriate term should be based on the context of the sentence and the desired tone the writer wishes to achieve.