For development purposes you can open an SQLite database in DB Browser for SQLite:
Open the keypairs table:
Select the private key blob, click “Export to file”:
The exported blob is a Transferable Secret Key, this is all you need to get the key out. public_key is redundant.
Same for importing, you can replace the private_key and public_key in existing profile. This is basically what the key import function did, but it also kept previous key as another row completely invisible anywhere in the UI. Replacing your identity key breaks group membership as your identity will change and you will write into existing chats with a new key which is not expected and usually displays as [The message was sent with non-verified encryption. See 'Info' for more details].