when interchangeable just isn't enough, there's interexchangeable. Same definition as interchangeable except with the ability to re-exchange/swap back and forth rather than a one off.
Excuse me sir, is this item interchangeable
Well actually, it's interexchangeable
Oh great, because i'd like to return it.
Ok here is your money back.
Ya know what, I changed my mind. Can I have it back?
Sure, here you go.