Overriding feature detection

We're currently building a page for deployment to a browser version that has a quirk in its FileReader API that results in errors when using the fetch polyfill, but in a way that means it passes the feature detection for blob support. Obviously this is such a specific problem that it wouldn't be sensible to change the feature detection in the upstream polyfill to take it into account, but ideally we'd like to avoid maintaining a fork just to tweak the feature detection.

Would it be reasonable to add some kind of mechanism for overriding the feature support for this use case? Happy to put in a PR with a candidate implementation if so.