Specifically, it adds an address into the wallet.

Easy to test now thanks to https://github.com/bitcoin/bitcoin/pull/14410
```
diff --git a/test/functional/wallet_importmulti.py b/test/functional/wallet_importmulti.py
index 9ba6860..bff37b2 100755
--- a/test/functional/wallet_importmulti.py
+++ b/test/functional/wallet_importmulti.py
@@ -95,6 +95,7 @@ class ImportMultiTest(BitcoinTestFramework):
         assert_equal(address_assert['iswatchonly'], True)
         assert_equal(address_assert['ismine'], False)
         assert_equal(address_assert['timestamp'], timestamp)
+        assert_equal(address_assert['ischange'], True)
 
         # ScriptPubKey + internal + label
         self.log.info("Should not allow a label to be specified when internal is true")
```

CKey key = DecodeSecret(strSecret);
        if (!key.IsValid()) throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Invalid private key encoding");
        CPubKey pubkey = key.GetPubKey();
        assert(key.VerifyPubKey(pubkey));
        CKeyID vchAddress = pubkey.GetID();
        {
            pwallet->MarkDirty();
            
            for (const auto& dest : GetAllDestinationsForKey(pubkey)) {
                pwallet->SetAddressBook(dest, strLabel, "receive");
            }
            
            if (pwallet->HaveKey(vchAddress)) {
                return NullUniValue;
            }
            
            pwallet->UpdateTimeFirstKey(1);
            pwallet->mapKeyMetadata[vchAddress].nCreateTime = 1;
            if (!pwallet->AddKeyPubKey(key, pubkey)) {
                throw JSONRPCError(RPC_WALLET_ERROR, "Error adding key to wallet");
            }
            pwallet->LearnAllRelatedScripts(pubkey);
        }
    }
    if (fRescan) {
        RescanWallet(*pwallet, reserver);
    }
    return NullUniValue;
}
UniValue abortrescan(const JSONRPCRequest& request)