I can address some of the points made in the post.
One point about the "artificiality": I think there's one fact that's often overlooked in the discussion of mRNA vaccines. SARS‑CoV‑2, for example, is a positive-sense single-stranded RNA (+ssRNA) virus. That means, the information that the virus uses to replicate itself and which describes the "blueprint" of its components, is stored as a single RNA. This RNA can more or less directly be translated into corresponding proteins by the ribosomes outside the nucleus, just like the mRNA used by mRNA vaccines. So, during a "natural" infection with such a virus, the virus's RNA also gets inside the cells and is translated into proteins, just like with the "artificial" mRNAs by vaccines! But the way this RNA enters the cell is somewhat different.
With viruses, they dock onto the cell and release their RNA into the cell. With mRNA vaccines like the one by BioNTech/Pfizer and by Moderna, this RNA is packaged into lipids (the stuff cell membranes are made of), which integrate more or less directly into the cell membrane and release the RNA. With vector vaccines like the Sputnik V or the Oxford–AstraZeneca vaccine, a different virus is used to carry the RNA load and infect cells (in the case of AstraZeneca, an adenovirus is used which usually infects chimpanzees and is normally harmless to humans). RNA in any case is degraded by the cells within a short time and leaves no traces.
Regarding the permanent modification of genetic information in humans: the genetic information in humans is stored as genomic DNA in the cell nucleus. DNA has a structure similar to RNA, but they do not work together, so RNA can't be simply integrated into the DNA. For DNA to form proteins, which make up most of the parts of a cell, it needs to be transcribed into RNA, which then is further processed into mRNA. This mRNA is tagged with a molecular export factor, which it needs to pass through the nuclear pore complexes, which are the highly specific transporters between the nucleus and the cytosol. After an mRNA has been exported from the nucleus, this tag is cleaved, so it can't return to the nucleus. Additionally, only if genetic information of egg or sperm cells is altered, this change is actually passed to the next generation.
So in summary: mRNA from vaccines behaves pretty much like the RNA inserted by RNA viruses into cells. And it can't find its way into the nucleus, where the genetic information is stored. And even if that happens by some way, it would first need to get "reversely transcribed" into DNA to be integrated. Some viruses can in fact do that, like HIV, which can also break into the nucleus in some instances (or wait for a cell division). Simple, "naked" mRNA of a vaccine however can't do that, only in extremely rare circumstances where the cell is already infected by another virus like HIV, I suppose.
But maybe you were talking about what is called "epigenetic modification", which is the molecular modification of the genomic DNA, where the actual stored sequence information is not altered, but the way it is read is modified. This process however is mediated for example by methylation of parts of the genome, for example, and does not intrinsically have anything to do with mRNAs in the cytosol. It should be noted that epigenetic modification is usually also reversible, not permanent, but it can be passed to the next generation, just like the genome itself.
What you said concerning the immune system focussing too much on another disease: I don't know a lot of immunology, but usually, building an immune protection against one pathogen also strengthens resistance against others. However, problems concerning the immune system most often arise when the immune system "overreacts" to an antigen and starts attacking parts of its own organism (autoimmune reaction). This can in fact be triggered by vaccines, even by only mRNA (and its protein products), as well as "natural infections", of course. Clinical studies are in place to analyze these occurrences.
