They can be interchangeable, but there is a slight difference in meaning. "go overboard" is the same as "go too far" in that you are overreacting, but there is also a sense with "go overboard" that you are "overexcited" or you are being a somewhat irrational in your reasons for overreacting. Whereas, with 'go to far' you are also overreacting, BUT you are not necessarily being irrational or overexcited.

The two phrases are very similar in meaning but have slightly different connotations. They both indicate something that is done in excess. "To go overboard" indicates that an action or activity is done in excess, generally with a sense of frivolity, superfluity or mindless exaggeration Example: "She went overboard with the Christmas decorations this year." "To go too far" also indicates an action done in excess but more with a sense of provocation, earnestness or unnecessary intensity Example: "He went too far when he insulted my mother." As a general rule, I would say that "to go overboard" has a lighter, more "silly" connotation whilst "to go too far" bears a greater sense of negative moral judgement