As far as I am aware, the current name would still be moved to ex_current, but you could use a second rename token to grab current back. if you had checked the redirect option it would be moved to ex_current but "current" would redirect to the new one and would not be available to use as a rename because it would technically still be "in use"
Unless there's another way around it I don't know, you will still need two rename tokens to accomplish it. You will still need that third journal. but if you didn't unselect the redirect no amount of renames/journal would let you rename to 'current' because IJ would consider it taken if it's redirecting to the new name.
If it's ex_current and not redirecting, you can still sort of access it; you will just have to use another rename token to turn a third journal into 'current'.
Wow this is confusing! No wonder you had so many questions.