@nprofile1q... As far as I can see there is a startup script that loads RSA keys from the config (I haven't found it, but it exists, I can configure an RSA key via the CLI and it's applied on the next reload replacing the RSA key in the image).
But the ed25519 and ecdsa keys in the image don't seem to be supported by the same flow, e.g. there is an "ip ssh server host-key rsa" command but no "ip ssh server host-key ed25519" command