Well, first, I would have to check and see if the synoynmous codons are important for virus reproduction. Second, this technique requires (AFAIK) lots of cell line viability testing and lots of tweaking. I don't think it's as simple as code swapping all the codons and then all the biology magically works the right way, biology is rarely that simple. Requires effort.

This sounds highly speculative then, i.e., the biology could never work out, no?

It depends on what you consider to be speculative. It's certainly not a product available to the mass consumer market, if that's what you mean. But that's also kind of an uninteresting fact, right?

"Synthetic genomes unveil the effects of synonymous recoding" https://www.biorxiv.org/content/10.1101/2024.06.16.599206v1

"Probing the limits of genetic recoding using multi-omics-guided evolution" https://www.nature.com/articles/s41467-026-74300-9

"Escherichia coli with a 57-codon genetic code" https://www.science.org/doi/abs/10.1126/science.ady4368

Speculative whether it could be done with humans without severe side effects that would make it useless/pointless.

Is it a product available to humans at all?