Directing edits to correct mutated sequences was first proposed and demonstrated in 1995.  This initial work used synthetic RNA antisense oligonucleotides complementary to a pre-mature stop codon mutation in a dystrophin sequence to activate A-to-I editing of the stop codon to a read through codon in a model xenopus cell system.  While this also led to nearby inadvertent A-to-I transitions, A to I (read as G) transitions can correct all three stop codons, but cannot create a stop codon.  Therefore, the changes led >25% correction of the targeted stop codon with read through to a downstream luciferase reporter sequence.  Follow on work by Rosenthal achieved editing of mutated mRNA sequence in mammalian cell culture by directing an oligonucleotide linked to a cytidine deaminase to correct a mutated cystic fibrosis sequence.  More recently, CRISPR-Cas13 fused to deaminases has been employed to direct mRNA editing.
In 2022, therapeutic RNA editing for Cas7-11 was reported. It enables sufficiently targeted cuts and an early version of it was used for in vitro editing in 2021.