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")
```

"may report that the imported key exists but related transactions are still missing, leading to temporarily incorrect/bogus balances and unspent outputs until rescan completes.\n"
            "\nExamples:\n"
            "\nDump a private key\n"
            + HelpExampleCli("dumpprivkey", "\"myaddress\"") +
            "\nImport the private key with rescan\n"
            + HelpExampleCli("importprivkey", "\"mykey\"") +
            "\nImport using a label and without rescan\n"
            + HelpExampleCli("importprivkey", "\"mykey\" \"testing\" false") +
            "\nImport using default blank label and without rescan\n"
            + HelpExampleCli("importprivkey", "\"mykey\" \"\" false") +
            "\nAs a JSON-RPC call\n"
            + HelpExampleRpc("importprivkey", "\"mykey\", \"testing\", false")
        );
    WalletRescanReserver reserver(pwallet);
    bool fRescan = true;
    {
        LOCK2(cs_main, pwallet->cs_wallet);
        EnsureWalletIsUnlocked(pwallet);
        std::string strSecret = request.params[0].get_str();
        std::string strLabel = "";
        if (!request.params[1].isNull())
            strLabel = request.params[1].get_str();
        
        if (!request.params[2].isNull())
            fRescan = request.params[2].get_bool();
        if (fRescan && fPruneMode)
            throw JSONRPCError(RPC_WALLET_ERROR, "Rescan is disabled in pruned mode");
        if (fRescan && !reserver.reserve()) {
            throw JSONRPCError(RPC_WALLET_ERROR, "Wallet is currently rescanning. Abort existing rescan or wait.");
        }