Whistle is one thing DO know about,and Yes you can play in any key on any whistle,though it does get complcated.One of my'poseur'pieces is
The Lark in the Clear Air,played on(Usually)an ordinary Generation C whistle,in six keys,starting in A and finishing in B flat,the only
octave jumps being the first note of the tune.Marge is correct,some tunes have to be played in the 'other'key to make them fit.That would be G on a D whistle with one flat,the note of concert C.