lights on a timer

Question

Rabbi: If I have a timer that turns the lights in my living room on or off and I decide that I don't want the light to go on when the pre set time comes, and I go to the light switch and put it in the off position so it won't turn on--can I do this on Shabbat? On Yom Tov? Secondly, if I have a pet{bird, dog,etc} and it gets hurt on Shabbat or Yom Tov can I violate Shabbat or Yom Tov to have it treated? Thanks for all your answers to my questions over the past year.