The SSD is a regular ol' m.2 slot. You do have to peel back the Lenovo sticker in order to unscrew it (Phillips). It doesn't say anything about warranty void if removed on the sticker, but remove at your own risk.

The SSD is a Samsung 961. Decent enough module. It is single sided, so I'm not sure if the standoffs will cause compatibility issues with double sided modules. The standoffs are plastic, so could be filed down if absolutely necessary.

There should be enough room for those thin "sticker" heatsinks, but not for anything more than a mm or two.