Thanks for your response, Nikhil!
So to clarify, we previously ran a test where showing A. marketing message vs. B. marketing message...having the A message actually positively impacted the C and D messages even though those stayed constant in both A vs. B experiences. Is your answer still the same in this case? Just want to be sure!
Unfortunately it is not possible to measure what you're looking for the way you described. Only the content present in the Mbox changes other data remaining the same. In your case I would recommend you decide on the content you want change in Experience A and B and finalize on it first.