Learn How to Downgrade
If you download Android 8.0 Oreo and you absolutely hate the changes and/or its performance, you should be able to downgrade to an older version of Android.
If this sounds like something you might be interested in, you should get familiar with the downgrade process before the Galaxy S7's Android Oreo update arrives. This way, you're ready.
Downgrading your Galaxy S7 from Android Oreo to an older version of Android will take time, particularly for those new to the process.
If you don't know how downgrading works on Samsung's phones, this guide from XDA-Developers will help get you started.