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")
```

"      \"timestamp\": timestamp | \"now\"                        , (integer / string, required) Creation time of the key in seconds since epoch (Jan 1 1970 GMT),\n"
            "                                                              or the string \"now\" to substitute the current synced blockchain time. The timestamp of the oldest\n"
            "                                                              key will determine how far back blockchain rescans need to begin for missing wallet transactions.\n"
            "                                                              \"now\" can be specified to bypass scanning, for keys which are known to never have been used, and\n"
            "                                                              0 can be specified to scan the entire blockchain. Blocks up to 2 hours before the earliest key\n"
            "                                                              creation time of all keys being imported by the importmulti call will be scanned.\n"
            "      \"redeemscript\": \"<script>\"                            , (string, optional) Allowed only if the scriptPubKey is a P2SH or P2SH-P2WSH address/scriptPubKey\n"
            "      \"witnessscript\": \"<script>\"                           , (string, optional) Allowed only if the scriptPubKey is a P2SH-P2WSH or P2WSH address/scriptPubKey\n"
            "      \"pubkeys\": [\"<pubKey>\", ... ]                         , (array, optional) Array of strings giving pubkeys that must occur in the output or redeemscript\n"
            "      \"keys\": [\"<key>\", ... ]                               , (array, optional) Array of strings giving private keys whose corresponding public keys must occur in the output or redeemscript\n"
            "      \"internal\": <true>                                    , (boolean, optional, default: false) Stating whether matching outputs should be treated as not incoming payments\n"
            "      \"watchonly\": <true>                                   , (boolean, optional, default: false) Stating whether matching outputs should be considered watched even when they're not spendable, only allowed if keys are empty\n"
            "      \"label\": <label>                                      , (string, optional, default: '') Label to assign to the address, only allowed with internal=false\n"
            "    }\n"
            "  ,...\n"
            "  ]\n"
            "2. options                 (json, optional)\n"
            "  {\n"
            "     \"rescan\": <false>,         (boolean, optional, default: true) Stating if should rescan the blockchain after all imports\n"
            "  }\n"
            "\nNote: This call can take over an hour to complete if rescan is true, during that time, other rpc calls\n"
            "may report that the imported keys, addresses or scripts exists but related transactions are still missing.\n"
            "\nExamples:\n" +
            HelpExampleCli("importmulti", "'[{ \"scriptPubKey\": { \"address\": \"<my address>\" }, \"timestamp\":1455191478 }, "
                                          "{ \"scriptPubKey\": { \"address\": \"<my 2nd address>\" }, \"label\": \"example 2\", \"timestamp\": 1455191480 }]'") +
            HelpExampleCli("importmulti", "'[{ \"scriptPubKey\": { \"address\": \"<my address>\" }, \"timestamp\":1455191478 }]' '{ \"rescan\": false}'") +
            "\nResponse is an array with the same size as the input that has the execution result :\n"
            "  [{ \"success\": true } , { \"success\": false, \"error\": { \"code\": -1, \"message\": \"Internal Server Error\"} }, ... ]\n");
    
    RPCTypeCheck(mainRequest.params, {UniValue::VARR, UniValue::VOBJ});