I'm a biochemist. mRNA doesn't rewrite parts of your DNA lol. You realize your DNA is constantly being transcribed into mRNA naturally right? If what you're saying is true, then by that logic, our DNA is constantly changing all the time.

You're confusing different processes. While it's possible for "complimentary" DNA to be changed by the process of reverse transcriptase with mRNA, it means little to nothing and your native DNA is still the same.