If I understand your question correctly, the answer is no you can not extend to 2 beats using the keyboard's Style Creature. The Yamaha Style Creator program will ask you if want to delete the notes in the style parts if you try to change them (except for the RHY2 section of the style).
The break button is always 4 beats long in each style. If the break you have is one beat and fade the other 3 beats (which is what I think is the issue). You need to search through the other styles on your keyboard and find a style with the break you want and then Copy and Paste it into your style.