First off, why?
Also, you would have to indicate if you are retaking the MCAT on the AMCAS (meaning update it) if you would like the score to be considered on this cycle. If you do not say anything, then the schools will not use the score on your application. That means if you have a 28 and get a 42 on the retake, schools will judge you on the 28.
Some schools may view it differently, but that depends on the school. What I mentioned above is what two secondaries told me (I don't remember which ones). I suggest contacting each school and how they view this.