It seems that Hyde does not yet do this, but I've made a fork and tried it out, and it works very nicely, so I'll make a pull request shortly after creating this issue.
I've also made a special accommodation for the Google font handling. If I'm overriding the font then I want not only to add a new link element; I also want to disable the unused font link.
While exploring how best to apply a few style overrides I ran across your suggestion about modifying a theme's head partial.
https://discourse.gohugo.io/t/how-to-override-css-classes-with-hugo/3033/4
It seems that Hyde does not yet do this, but I've made a fork and tried it out, and it works very nicely, so I'll make a pull request shortly after creating this issue.
I've also made a special accommodation for the Google font handling. If I'm overriding the font then I want not only to add a new link element; I also want to disable the unused font link.
Thanks so much for the great theme!