Sadly, I think if you want to do a sudden change in unchartered territory it is best to do a strand test first.
That way you aren't stuck with anything you won't want to live with. And, as far as I know, what will happen with old dye is that it just won't work as well. Just like if you leave Hydrogen Peroxide sitting in your counter for ages, after years and years it will become less effective.
But don't take my word for it because I am not 100% sure. Do a strand test and see how it goes.