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")
```

{
    std::shared_ptr<CWallet> const wallet = GetWalletForJSONRPCRequest(request);
    CWallet* const pwallet = wallet.get();
    if (!EnsureWalletIsAvailable(pwallet, request.fHelp)) {
        return NullUniValue;
    }
    if (request.fHelp || request.params.size() != 1)
        throw std::runtime_error(
            "importwallet \"filename\"\n"
            "\nImports keys from a wallet dump file (see dumpwallet). Requires a new wallet backup to include imported keys.\n"
            "\nArguments:\n"
            "1. \"filename\"    (string, required) The wallet file\n"
            "\nExamples:\n"
            "\nDump the wallet\n"
            + HelpExampleCli("dumpwallet", "\"test\"") +
            "\nImport the wallet\n"
            + HelpExampleCli("importwallet", "\"test\"") +
            "\nImport using the json rpc call\n"
            + HelpExampleRpc("importwallet", "\"test\"")
        );
    if (fPruneMode)
        throw JSONRPCError(RPC_WALLET_ERROR, "Importing wallets is disabled in pruned mode");
    WalletRescanReserver reserver(pwallet);
    if (!reserver.reserve()) {
        throw JSONRPCError(RPC_WALLET_ERROR, "Wallet is currently rescanning. Abort existing rescan or wait.");
    }
    int64_t nTimeBegin = 0;