Yes. You can create your own styles for Yamaha keyboards using an ordinary sequenzer software. The Yamaha style files are actually renamed midi files with some added formatting.
It is a little hard to explain shortly, but read mine and others articles at http://home7.inet.tele.dk/js/740pages
There are lots of links to style sites and style software too.
Happy styling
Jørgen
The Unofficial Yamaha PSR 740 Home Page