1. Yes, you would need to reinstall the operating system every time you change SATA modes.
2. If no RAID mode, there is no need to have Intel® Rapid Storage installed. The driver that controls AHCI or RAID stays on the operating system.
The latest version compatible for Windows® 10 Download Intel® Rapid Storage Technology (Intel® RST) RAID Driver
Rather than switching Modes and reinstalling the OS, I think I will opt for uninstalling RST.