Will the var members in case class affect case class's equality?

I have made heavy use of case classes in my code, replying on the underlying equality definitions of case class to behave correctly. Then now I found that I need to add another field member to a case class.

1. So if I add a var field member in case class, will it mess up the equality attributes for the case class?
2. If 1 is yes, then what if I just change the var field value once, after that, no any reassignment will happen, before the case class goes into any collections or do equality comparison, will that still mess up the equality behaviors?