Is "covered in" here interchangeable with "covered with"?
Yes, generally the verb "covered" can be followed by either the preposition "in" or "with" to form a phrasal verb. So "covered in" and "covered with" are usually interchangeable. Sometimes, they can have slightly different nuances, however, this doesn't ever affect the overall meaning. You can use either "covered in" or "covered with" in these examples: Ex: The dog is covered in mud. Ex: The sky is covered with clouds.