i can't fathom how you can even mess with dna/rna
Science, bitch.
You use chemicals that do the same thing but are much stronger than the enzymes which produce the splicing naturally (note that 80% of the reactions in our body are caused by weak chemicals. For example, to add an H, the body usually uses vitamins. You can use a strong acid such as sulfuric or chlorhydric acid to add the H and both are much stronger than the weak organic acids we intake with our meals.) and by knowing which chemicals we add and in what order, we can estimate which nitrogen base (The letters A, C, G, T/U) will be removed with its nucleotide.
Of course it isn't 100% fail-proof which is why these are vaguely documented as not much research was put in place.
Although splicing is what we're going to do through the year, this thesis is for eukaryotic cellular reproduction.