I want to change a spot light's attributes over time: I want to change its "Spot Shape": including both Size and Blend. Is this possible? If so, HOW?
There certainly is, it can be animated as pretty much any other regular blender property.
Just place your cursor over the slider value for the Size or Blend factor properties, and press I to add a key frame.
Move the current frame to the desired point in time, then change value of the Size or Blend factor for that frame and with cursor hovering the slider value press I again to add a new keyframe. Repeat for as many steps necessary to accomplish all your animation. Press play to verify your animation.
You can keyframe just about any property by hovering over it with your cursor and pressing I.
Just go to the frame where you want the animation to start, set the value you want it to start at, and hit I with your mouse over the property. Then go the the frame where you want it to end and repeat the process with the ending value.