I can go into more detail about parts of this at least. There are several parts to mRNA. The two that are brought up here are basically the coding sequence (CDS) and the 3' untranslated region (3'UTR). The CDS is what is used to make the protein, and the 3' UTR is not used to make the protein but instead is meant to regulate the stability of the mRNA and regulate how much protein is made. There is another class of RNAs I have to mention as well: non-coding RNAs (ncRNAs). These are RNAs that do not make protein, but rather the RNA itself performs some sort of function. So it sounds like for AES they took the 3' UTR (which normally shouldn't make protein) and put it after the stop codon for the spike protein. As long as they didn't fuck it up, there shouldn't be a risk of the AES 3'UTR specifically fucking anything up. But it gets a lot more complex.
mtRNR-1 is one of those ncRNAs, specifically a type known as a ribosomal RNA (rRNA). Like I said, it has functions itself. This seems to me like a terrible idea to put into a mRNA. The big question I have is how much of the mtRNR-1 gene is in the sequence (based on the paper it sounds like 142 of the 959 nt, though the more important question is which nucleotides)? The mutations in this ncRNA actually change its structure and function, and it looks like
that is how the mutations cause hearing loss (disclaimer, I can't read this whole article now for info beyond the abstract. If anyone wants I can try and get access later).So it sounds like Pfizer took some part of a ncRNA that can cause issues when mutated/modified, and threw it in with the spike protein sequence, not knowing how the spike protein sequence would affect the ncRNA sequence. This means that the mRNA itself may (emphasis on may) be dangerous. Could this result in the deafness? Possibly, though that would need research to be done. With the dangers of the spike protein and the reports of autoimmune disorders, I would honestly lean more towards the spike protein and immune response fucking up their hearing instead. But I can't believe that they wouldn't see an issue with putting ncRNA sequences into an experimental drug (or more likely they just ignored the potential issue).
Lastly I'll mention the pseudouridine. As a side note with the last paragraph, inserting pseudouridines can influence not only RNA stability, but RNA structure, which is again something you have to be incredibly careful about when working with a ncRNA, especially one where changes in structure result in pathologies. As for what is said in the post, it looks wells supported that
pseudouridine results in stop codon readthrough in yeast. My understanding is that they did not insert the pseudouridine at designated locations, and instead if they inserted it randomly into a stop codon then a bunch of extra junk may get turned into protein (though it is also very possible that the ribosomes could recognize something is wrong and abort making the protein altogether. It's impossible to say without knowing the sequence in question, which is why it's important to test these things). If that is the case, I would hazard a guess that we have little to no idea what would get made. Neither the 3' UTR of AES or any of mtRNR-1 are meant to be made into proteins. So you wouldn't really end up with spike+AES+MTRNR1, but rather spike+junk+junk, with the junk maybe being harmless or maybe being dangerous, we wouldn't have any idea without knowing what the junk is and studying what effects it had.
As for pseudoruridine, cytochrome c, and mitochondria, what you just posted is an excellent explanation and I don't think I need to make things more confusing by trying to overexplain it. Everything I just wrote is probably too much for a lot of people anyways though I'm happy to answer questions. It really seems like all bets are off for what these shots can do to people.