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")
```

if (!request.params[1].isNull())
        strLabel = request.params[1].get_str();
    
    bool fRescan = true;
    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");
    WalletRescanReserver reserver(pwallet);
    if (fRescan && !reserver.reserve()) {
        throw JSONRPCError(RPC_WALLET_ERROR, "Wallet is currently rescanning. Abort existing rescan or wait.");
    }
    
    bool fP2SH = false;
    if (!request.params[3].isNull())
        fP2SH = request.params[3].get_bool();
    {
        LOCK2(cs_main, pwallet->cs_wallet);
        CTxDestination dest = DecodeDestination(request.params[0].get_str());
        if (IsValidDestination(dest)) {
            if (fP2SH) {
                throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Cannot use the p2sh flag with an address - use a script instead");
            }
            ImportAddress(pwallet, dest, strLabel);
        } else if (IsHex(request.params[0].get_str())) {
            std::vector<unsigned char> data(ParseHex(request.params[0].get_str()));
            ImportScript(pwallet, CScript(data.begin(), data.end()), strLabel, fP2SH);
        } else {
            throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Invalid Bitcoin address or script");
        }