1. Yes
2. Warranty? Follow the guidelines. No warranty needed if you follow the tutorial.
3. It's recommended to reinstall OS if you're banned in COD:MW Warzone. So I can not speak directly for Apex in this case, but if you want to make sure to clean all the traces, you can also reinstall here.
If not installed already, Win 10 Build 1909 is required for the spoofer to work accordingly.