I am working on a PGP scheme where a private key is created offline (and in volatile memory) and must be reused on very rare occasions to sign a piece of exportable data. The private key is locked using a random passphrase with ~256 bits of entropy, and the passphrase and resultant PGP secret key are written on paper and locked up for later use. The key needs to remain usable for years in the future.
To simplify the future import procedure by reducing the amount of manually entered data, would it be safe to publicly export the secret key file provided the passphrase is kept locked up? That way, the secret key can be imported off of a flash drive or similar, while only the passphrase needs to be keyed in.