➤ mv ~/.gnupg/ ~/.gnupg.orig
                                                                                                                                                                         
➤ ssh k4 cat ~/.gnupg/gpg-niklas-hambuechen-0x2DFBFA03-secret-subkeys.asc | gpg2 --import
gpg: directory '/home/niklas/.gnupg' created
gpg: new configuration file '/home/niklas/.gnupg/dirmngr.conf' created
gpg: new configuration file '/home/niklas/.gnupg/gpg.conf' created
gpg: keybox '/home/niklas/.gnupg/pubring.kbx' created
Enter passphrase for key '/home/niklas/.ssh/id_rsa': 
gpg: /home/niklas/.gnupg/trustdb.gpg: trustdb created
gpg: key 2DFBFA03: public key "Niklas Hambüchen <niklas@nh2.me>" imported
gpg: To migrate 'secring.gpg', with each smartcard, run: gpg --card-status
gpg: key 2DFBFA03: secret key imported
gpg: Total number processed: 5
gpg:               imported: 1
gpg:       secret keys read: 5
gpg:   secret keys imported: 3

diff --git a/g10/import.c b/g10/import.c
index 1ed40a63c..91ff0c8ec 100644
--- a/g10/import.c
+++ b/g10/import.c
@@ -2706,6 +2706,20 @@ transfer_secret_keys (ctrl_t ctrl, struct import_stats_s *stats,
           goto leave;
         }
 
+      if (!force)
+        {
+          int already_exist = agent_probe_secret_key (ctrl, pk);
+
+          if (already_exist == 1)
+            {
+              err = gpg_error (GPG_ERR_EEXIST);
+              goto exist;
+            }
+          else if (already_exist == 2)
+            /* It's a card stub.  */
+            force = 1;
+        }
+
       if (ski->is_protected)
         {
           char countbuf[35];
@@ -2790,6 +2804,7 @@ transfer_secret_keys (ctrl_t ctrl, struct import_stats_s *stats,
         }
       else if ( gpg_err_code (err) == GPG_ERR_EEXIST )
         {
+        exist:
           if (opt.verbose)
             log_info (_("key %s: secret key already exists\n"),
                       keystr_from_pk_with_sub (main_pk, pk));

diff --git a/g10/import.c b/g10/import.c
index 1ed40a63c..345e8cc75 100644
--- a/g10/import.c
+++ b/g10/import.c
@@ -2955,9 +2955,23 @@ do_transfer (ctrl_t ctrl, kbnode_t keyblock, PKT_public_key *pk,
 {
   gpg_error_t err;
   struct import_stats_s subkey_stats = {0};
+  int force = 0;
+  int already_exist = agent_probe_secret_key (ctrl, pk);
+
+#ifndef OK_TO_CHANGE_ERROR_BEHAVIOR
+  if (already_exist == 1)
+    return gpg_error (GPG_ERR_EEXIST);
+#endif
+  if (already_exist == 2)
+    {
+      if (!opt.quiet)
+        log_info (_("key %s: card reference is overridden by key material\n"),
+                  keystr_from_pk (pk));
+      force = 1;
+    }
 
   err = transfer_secret_keys (ctrl, &subkey_stats, keyblock,
-                              batch, 0, only_marked);
+                              batch, force, only_marked);
   if (gpg_err_code (err) == GPG_ERR_NOT_PROCESSED)
     {
       /* TRANSLATORS: For a smartcard, each private key on host has a

gpg: Anzahl insgesamt bearbeiteter Schlüssel: 1
gpg:                             unverändert: 1
gpg:              gelesene geheime Schlüssel: 1
gpg:            geheime Schlüssel importiert: 1

[...]
gpg: sec  brainpoolP384r1/458612006D8E6F0D 2023-03-08  Berta Boss <Berta.Boss@demo.gnupg.com>
gpg: Schlüssel 458612006D8E6F0D: "Berta Boss <Berta.Boss@demo.gnupg.com>" nicht geändert
gpg: Schlüssel 458612006D8E6F0D/458612006D8E6F0D: geheimer Schlüssel bereits vorhanden
gpg: Schlüssel 458612006D8E6F0D/FFA2FCCB2EC589F8: geheimer Schlüssel bereits vorhanden
gpg: Schlüssel 458612006D8E6F0D: geheimer Schlüssel importiert
gpg: Anzahl insgesamt bearbeiteter Schlüssel: 1
gpg:                             unverändert: 1
gpg:              gelesene geheime Schlüssel: 1
gpg:                 unveränderte geh. Schl.: 1
gpg: keydb: handles=3 locks=1 parse=3 get=3
gpg:        build=0 update=0 insert=0 delete=0
gpg:        reset=0 found=3 not=0 cache=0 not=0
gpg: kid_not_found_cache: count=0 peak=0 flushes=0
gpg: sig_cache: total=10 cached=8 good=8 bad=0
gpg: random usage: poolsize=600 mixed=0 polls=0/0 added=0/0
              outmix=0 getlvl1=0/0 getlvl2=0/0
gpg: rndjent stat: collector=0x00000000 calls=0 bytes=0
gpg: secmem usage: 0/32768 bytes in 0 blocks