Music written for penny whistle is the same for any pennywhistle.

Don't re-write anything written for a D - or any other whistle. To change keys, you use the same music and change whistles.

If you use a different whistle, it will sound in a different key, but the notation tells you which fingers to use - and doesn't care which whistle you use.

For melody lines written in random keys, you would usually transpose to D, (two sharps) as if you were playing it on a D whistle, since the tonic scale on any whistle is in the "two sharps" mode. Once written for whistle the same score may be used with any whistle if you just "pretend" you're playing the D one.

More advanced players may actually transpose, but for a beginner you can just assume that music for whistle is music for any whistle.

John