Is it possible to change BIOS settings on bare metal instances?

AWS EC2 Bare Metal instances do not provide direct access to the BIOS or the ability to modify BIOS settings in the same manner you would with an on-premises physical server. When you use a bare metal instance on AWS, you're renting the entire physical server, but AWS abstracts away certain hardware-level configurations, including BIOS, to ensure stability, security, and performance.

The primary value proposition of AWS's bare metal offering is to provide direct access to the hardware for applications that need it, such as those requiring specific hardware features or for running specialized hypervisors. However, the control is not as granular as having your own server on-premises where you can access the BIOS.

If AWS did allow BIOS modifications, it would introduce risks that users could change settings that could potentially destabilize the hardware or reduce its performance. By abstracting this layer, AWS maintains a consistent hardware baseline across all instances of a specific type.

As for persistence of any settings, in general, if you stop and start an EC2 instance (regardless of whether it's bare metal), any changes you made within the operating system or installed software will persist. However, transient settings (like in-memory data) will be lost. But since you cannot change BIOS settings, this question is somewhat moot in this context.