Following the [Debian tutorial on subkeys][1] I like to create a keyring with a primary key (SC) and two subkeys (E and S) and then export and remove the secret primary key. However I struggle to re-import the exported secret key in case I want to revoke and renew the subkeys.

Initial setup with two subkeys

	pub  1024R/158C07CE  created: 2015-09-21  expires: never       usage: SC
						 trust: ultimate      validity: ultimate
	sub  1024R/588AC467  created: 2015-09-21  expires: never       usage: E
	sub  1024R/3637E2AA  created: 2015-09-21  expires: never       usage: S
	[ultimate] (1). Foobar

	$ gpg -K

	sec   1024R/158C07CE 2015-09-21
	uid                  Foobar
	ssb   1024R/588AC467 2015-09-21
	ssb   1024R/3637E2AA 2015-09-21

	# sec means the secret is still there

Export primarykey-only, export subkeys-only, remove secret keys, and re-import subkeys

	$ gpg --export-secret-keys 158C07CE! > primary.sec
	# secret-keys with exclamation mark just exports primary keypair
	$ gpg --export-secret-subkeys 158C07CE > subs.sec
	$ gpg --delete-secret-keys 158C07CE
	$ gpg --import subs.sec
	$ gpg -K

	sec#  1024R/158C07CE 2015-09-21
	uid                  Foobar
	ssb   1024R/588AC467 2015-09-21
	ssb   1024R/3637E2AA 2015-09-21

	# sec# means the secret key is missing (this is what I want)

Now I want to re-import the primary secret key

	$ gpg --allow-secret-key-import --import primary.sec

	gpg: key 158C07CE: already in secret keyring
	gpg: Total number processed: 1
	gpg:       secret keys read: 1
	gpg:  secret keys unchanged: 1

What? Why?

	$ gpg -K

	sec#  1024R/158C07CE 2015-09-21
	uid                  Foobar
	ssb   1024R/588AC467 2015-09-21
	ssb   1024R/3637E2AA 2015-09-21

Here is useful [Stackexchange article on which keys GPG exports in which case][2]

  [1]: https://wiki.debian.org/Subkeys
  [2]: https://unix.stackexchange.com/questions/207815/which-keys-gpg-exports-and-what-is-in-the-keyrings