Nuxt does not support hybrid SSG or SSR modes, hence why this is defined globally and not per component.
At the end, performance should be as good with either SSG or SSR and you can probably generate most of your content with SSG.

More rendering modes will probably be announced during NuxtNation so feel free to join.

In the meantime, I know that Next.js does have some flexibility in the way that it allows to still request some routes from the server (not only using client-side queries).
It is called getServerSideProps (Server-side Rendering) and you can get more context in this Twitter thread.

Nuxt do not have this kind of thing tho.