test.py

from kivy.app import App
from kivy.factory import Factory
from kivy.config import Config
from kivy.clock import Clock
from functools import partial


def callback(instance, *args):
    print 'icon change'
    instance.icon = 'icon2.png'
    Config.set('kivy', 'window_icon', instance.get_application_icon())


class BejotoApp(App):
    icon = 'icon.png'
    title = 'Test icon'

    def build(self):
        Config.set('kivy', 'window_icon', self.get_application_icon())
        Clock.schedule_once(partial(callback, self), 2)
        return Factory.Button()

if __name__ == '__main__':
    BejotoApp().run()