battery and top case
If I want to change the battery of a Macbook Pro 15' 2017, does Apple replace also the Top Case?
MacBook
It depends. If the work is done at the Apple Store or at the AASP's shop, then the whole Top Case is replaced. If the laptop is sent out to an Apple repair depot, then I'm not sure what Apple does these days.
Apple does have a multiple free repair programs for battery related issues. Some are publicly acknowledged here and others are not publicly acknowledged. Apple also has a free repair program for keyboard related issues as well.