Were mRNA COVID vaccines expensive? Not like 100s of $. And there is mRNA platform developed by some European researches for controlled expression of the reprogramming genes. And in animal studies there were almost no adverse effects when this biotech was applied partially and in a time-controlled manner.

The only caveat may be types of tissues with rapid cell exchange or which already regenerate well, as the liver, for example. But it should be possible to bypass this by proper design of the treatment.