Just because I’m not a skilled enough developer to code Linux from scratch doesn’t mean I can’t make a patch for it.
Also doesn’t guarantee that I won’t generate unintended consequences
Point being - you don’t have to be capable of making the whole to make modifications. (But in any complex system, there are likely to be unintended consequences)
A good example would be immune modulation for cancer therapy - ipilimumab and it’s ilk are miracle workers for many, however because of the complexity of the immune system in a proportion of patients there is a cascade of multi organ failure kicked off by the treatment
Which is why the idea of using something like Crispr to mess with genes is fraught with so many unknown issues and risk.