You can't directly access the classNames of child components i.e. if the component is composed of an <h1> inside of a <div> (with <div> being the top-level component), you cannot directly set the className of the h1 if a prop doesn't exist to do so
But you can set the classname of the component and then refer to it as ".componentclass h1" or similar, right? Or is that what you are saying gets too unwieldy?
Using ".component-name <insert child tag>" goes against semantic UI conventions and couples your custom styles to the tags instead of the classes in the component. It quickly becomes brittle when trying to update those styles if the tags change in an updated version, or if the rendered output changes structure, etc.
Maybe it's time to rethink your conventions...? The solution to your problem is in front of you, but you're avoiding implementing it because of strict adherence to arbitrary conventions.
