Could there be some kind of molecular editing system ? What tools could be devised to work with genes? Could scientists then create tailored DNA molecules

Yes. there already is, scientists can genetically modify plants by adding or removing genes to make them different such as make a corn stalk have 4 ears instead of 2. but also breeding like dogs and other animals is a form of molecular editing because they essentially cause a gene mutation that alters the gene sequence and created a tailored DNA molecule. like a golden doodle dog is a genetic modification of a golden retriever and a poodle it wasn’t a natural combination to begin with if you want to get into technicality’s all domesticated animals are genetically modified. BUT the plant example about GMO plants& foods is probably the best example. they can also make plant that have pesticides in their dna so they don’t have to spray them but they’re super toxic to humans and animals that eat them.