Not exactly your question, but my reading of The Gene: An Intimate History says any microbiome changes from eating fermented foods like yogurt/kefir/kimchi disappears when the food leaves ones diet. This was published in 2015 so could be superceded by subsequent studies in same field and I didn't bother researching the studies referenced in the book, either. The book also talks about successful uses of fecal matter transplants (FMT) for c. difficile treatment, and it worked about 90% of the time, but required a periodic refresh because none of the patients in the studies could maintain the healthy microbiome without the FMT after a year or so.