There are many ways to create genomic changes. One of the denials was based on the "backbone" approach, which is starting with a virus, deleting genes and adding others in using sequencers and CRISPR technology.
This conforms to the "blueprint" model of DNA, with humans acting as incompetent architects. Most of the organisms produced in the fashion are non-viable, and at substantial capital and labor costs.
The indications are they used a more cost-effective means of stimulating changes using biological tools. You can force species jumps by transfusions of filtered blood components. This will cause rapid mutations to adapt. This is documented at WIV.
You gradually jump across intermediate species between bats and humans starting with the world's largest collection of bat viruses. These are fever resistant viruses because bats have 45°C body temp, also civet cats and dogs are between bats and humans. Pangolins are below humans at 26.5-34.5°C.
You can also force gene replacement by co-infecting lab animals with other viruses with new function genes, also by blood fraction injections. When two viruses infect the same cell, they will swap genes.
These processes can produce thousands of variations, which are then selected by the immune systems of the hosts for viable mutations. Every lab animal therefore replaces thousands of laboratories trying genetic variations, and bringing forward the most efficacious ones. Multiply this by dozens or even hundreds of animals, and it is far more capability than all the researchers in the world.
You could also enable this process by modulating the immune systems of your test animals to make them more susceptible to infection, and try anti-viral drugs on them to produce resistant virus strains.
Further, all of this would not produce a "fingerprint" of human intervention, because it is co-opting natural processes.
It also reveals the EXTREME HAZARD of GMO organisms, because every gene splice human make for "beneficial gain of function" potentially disrupts the unimaginable, uncountable, untestable complexity of genetic stability and resilience that has been developed by Nature by running septillions of genetic experiments per second for the last 4 billion years, through mass extinctions that could have been from earlier global genomic instabilities.