first: i dont think that falsification is the only test for scientific claim. i think that any scientific claim that we can test is scientiifc. including the abillity to prove it and not only to falsify it. second, we cant flasify evolution either, so i see no difference.
and how you suggest to do that? you need to suggest such a test to check it. if you cant then we cant test this idea either.
and how do you know that? how you can prove that if we see 2 fins of 2 different fish its not the result of convergent evolution? (or convergent design). if we cant prove that it will be just an assumption.