Changing a single instance of an icon

The API for changing icons globally has been wonderful with the small exception that in some spots I want to use a different style/weight (generally due to being bigger or smaller) but I can’t figure out how to select icons in specific spots.

For example: With the chat icon, I would like to use a linear icon in the topbar, but a filled icon in the dropdown user menu.

The API changes both without differentiation. Is there a way I can target them individually in the script, or should I use CSS for one of them instead? My hesitation with using CSS is that it seems like the API change is seen as the proper way.