You cannot "generate evidence at will to meet any threshold of evidence" for this specific example ("all swans are white") because, unless you posit that there are swans in Kepler-422B, I can set my threshold of evidence to "we have turned the earth into computronium and have not found any non-white swans", which is a finite (albeit large) threshold.
Once we agree on whatever definition of "swan" we care about (an animal belonging to a specific phylogenetic branch, with such and such qualities) we can agree on a more reasonable threshold, one that should include a visit to Australia to be crossed.
Once we agree on whatever definition of "swan" we care about (an animal belonging to a specific phylogenetic branch, with such and such qualities) we can agree on a more reasonable threshold, one that should include a visit to Australia to be crossed.