Is it best to convert the Yamaha Style File to Midi first then the Midi to Korg Style.

Or straight conversion through styles works?

If you have Style Works you can convert without transfer via or create midi first.
Whatever way, there always some tweaking needed to make it sound personal or similiar as the original.
I've experienced that to convert within same brand often give better result "as is" than from one brand to another.

It it possible to copy parts of a style variation to another ie variation 4 to 1? Via the keyboard or does this have to be done via external sequencer.

I am not familiar with Style Works but is very intriguing to me. Do you downloa/buy the XT version named for the keyboard you have, or for the styles you want to import? I want to get Yamaha t2 styles for my Korg PA500. And what's the best site to get the package at?

You can normally only get it from the manufactures site.

Get the version for your keyboard, unless you will be changing to a different manufactures keyboard in the future, which if that is the case get the universal version. (More Expensive)

Hope this helps

Bill

I use Styleworks Xt but not always successful.