It's not like these things people have done are exactly safe and side-effect free already. People have:
* Made entire species extinct through hunting and deforestation
* As a side effect of industrialization, dumped enough CO2 to change the climate and will probably keep it up
* Domesticated multiple other species into being dependent on us, from crops to farm animals to dogs
* Started work on AI and machines which might even replace us one day
Genetic modification isn't a one-way street to destruction as much as AI is, or industrialization.
Also regarding perpetuating life: the one thing life has in common is that it perpetuates itself. We'd be a shitty species if we perpetuated machines or microbes instead of ourselves.
> Who knows where it'll go, but homo sapiens isn't equipped to be space-faring or even survive on this planet beyond a few billion years.
So? I don't see how that's an argument for human genetic engineering. If we want to perpetuate life throughout the universe for some reason, we can send probes loaded with microbes, maybe even advanced probes that can incubate more advanced animal and plant species to create an ecosystem. In your scenario, humanity is presented with its extinction through either natural causes or by being the architect of its own destruction. I'd prefer the former.