Epigenetics is real but the version which is being hyped in the alternatives/supplements market - such as how it enables your mind to reprogram your genes or, as you describe, "flip the switches" on the genome from unhealthy to healthy - is mostly bunk mixed with a rather large dose of magical thinking.
Epigenetics is a very complex subject and it's best to let a scientist answer that question. In a blog posted by Dr. Dave Woynarowski, MD, who is very well known in the field of anti-aging medicine, he says epigenetics means “around or surrounding the genome”.
"The study of epigenetics results in the science of gene expression patterns, heritable through cell division, that is independent of DNA sequence. In other words, stuff that acts like genes but isn’t! . . . (T)his 'around the genome' bit structurally refers to the scaffolding matrix that holds our genetic material DNA in tightly wound packets. It refers to the proteins that surround and are part of that scaffolding and interact with our DNA, some of which actually let pieces of it unwind, for copying purposes. . . . (Y)ou should know that, while I am going to stress how much you can change your physical fate and outcomes by altering your epigenetics, you should understand that a large part of your epigenome is not something you want to change, as it is responsible for genetic stability and lends structural soundness to your DNA."
So what does all this mean in plain English? Simply put, we are not locked into all of our genes. What we can change about these genes is which ones get read and result in obesity, diabetes, heart disease, cancer, and a variety of inflammatory diseases.
"Epigenetics allows a huge variation in which genes are actually read and which ones are not," Dr. Dave explains. "Functionally, this means your environment, which is primarily how YOU treat YOU, determines your fate, not your genes. As a matter of fact, the 80/20 rule applies here. You have control over about 80% of your health just by how you eat, sleep, deal with stress, exercise, etc. Your exposure to toxins, radiation, etc. counts as well, but for most of us, it’s the stuff we do every day that matters most. Recent studies have shown that one healthy meal and one bout of exercise can positively improve your epigenetics by altering which genes are read and not read."
In other words, there's no need for an epigenetics supplement, although Dr. Dave jokingly predicts later in the same blog that "It’s also probably only a matter of time before some slick marketer starts using the term epigenetics to sell supplements as well."
As he explains, "Almost all supplements act via epigenetics. Fish oil and Vitamin D are two examples, although fish oil also acts directly on membranes, ion channels, mitochondrial biochemistry and of course telomeres as well. Most other supplements, worth their salt, alter genetic expression by changing and altering the epigenetic matrix."
But I wanted more sources for this information and checked for some corroborating information. I found it here, although this site is much more technical.
From what I have read, my guess is that you're wasting your money on these supplements.
As for John Paul II having used it, just about everyone who wants to sell the latest version of snake oil to a Catholic consumer says John Paul II took it. (Mother Theresa is a close second.) My response to that is simple: "Prove it."
And even if he did, so what? Ten years ago, Vitamin C was all the craze for colds until they discovered that zinc actually works better. Now they're questioning fish oil supplements and probiotics - all supplements that JPII might have taken during his lifetime. The point is, it doesn't prove that they work, just that he took them as did millions of other people who did so based on the current science of the day.
But things change. Science changes. It advances, learns more, and continually refocuses itself, as it should.
After researching the answer to this question, I could not be persuaded to purchase an epigenetic supplement no matter how slick the marketing.