E.G. Take care when ——— prototype X not to override this attribute.
My ideas are evolving, which feels sort of pretentious, and adapting, which just seems vague. Deriving might work, but might also be confusing since it is commonly used when discussing classical inheritance.
The term extending might be applicable, but seems to imply that the original object is being modified, which is not the case here.
Underscore.js seems to make this available via e.g.
Is there a succinct and widely used term for this procedure?