By arrows, are you referring to when a notebooks tabs exceed the width of the parrent and arrows appear to allow you to scroll? If so--there is no way to change them that I know of, however, you can turn the scrollablility off completely using...
scrollable : if True scroll arrows should be added
The set_scrollable() method sets the "scrollable" property to the value specified by scrollable. If scrollable is True the tab label area will have arrows for scrolling if there are too many tabs to fit in the area.