It has a different chemical compostion make up than the interior paint.Which I have heard that can make your interior paint fail in time,how long is unsure to me.If you are doing this then use a exterior paint to go along with this.What this will do is make sure you have the paint that goes with the primer you are using.
I wouldn't recomend doing your whole windows like this for the ext. paint has a little less sheen to it.I tell you what though your window sashes will be pretty durable.
Again use ext paint with ext primer or your paint may let loose.
I have seen actually quite a few home owners do or ask the same thing,to save time,open the window and hit the sides top and bottom.
You will be ok.

You would not want to use an exterior paint inside because of the mildecide can cause respiratory problems.
So stick with interior paint for the inside of your house and exterior for the outside.

Maybe in large quanities,but seeing as how you are going to use maybe a quart of paint for your whole project,you do the painting however you feel fit.

Exterior paint is also a softer finish than interior paint, so it can flex with temperatures. Interior paint is designed to be a harder finish.