I am not familiar with your model keyboard but to modify styles you need a sequencer keyboard where you can adjust 'tweak' every single channel and save it. These keyboards are usually the 'bigger' and more expensive boys.
But I am sure you can load one ore more external styles into you board.
If you go to svpworld.com (click download software) you can download for free a few programs created by 'the master' Michael Bedesem. Also on www.jososoft.dk you will find good programs for free.
Style Creator, Midiplayer and Style Updater and a few others are VERY handy programs.
You have to install the whole program first on your computer and than the latest update over it!
With these programs you can 'tweak' a style, save it on your computer, floppy, smartcard or USB-stick and than load it in your keyboard.
I hope this puts you on the right 'track'.
Let us know so other people on this friendly forum can also benefit from it.
Regards
Dick Rector
Bali