We use a “sliders” icon here by default (and it’s the only occurrence of this icon in Discourse by default) — so it would be safe to use replaceIcon() in this case
Because we don’t have an API to replace individual icons, the best way we can support this today is by evaluating requests to add new aliases that group similar use cases.
So for example, we use d-liked as an alias for heart so replaceIcon() can be used against d-liked to change it in the like context, rather than replacing every occurrence of the heart icon throughout the app.
It would be nice to replace any single occurrence though, that’s not an unusual situation in themes — hopefully someday we’ll have an API for that.