Set non-volatile key in MAX 10 devices to OTP

We want to use a MAX 10 for our design, but there are still some open points regarding security features, especially regarding the non-volatile encryption key.

If the key was written, can it be erased again, for example by a full chip erase? Or can it be set to OTP?

The datasheet says it can be erased, but I also received some information that it can not. Can someone confirm one or the other possibility?

Thanks a lot in advance!