I have flown two types where power-backs were both approved in the FCOM and allowed by SOP. Other SOPs that I have operated with permitted one engine shut down during taxy-in and my current four engine type allows two engine shut down - but the engines that run the hydraulics must be kept running until brakes are parked. This is called CDF (common dog f...).
I have never flown a type where coasting with all engines off was permitted. Doing this is called a CLM (career limiting move).