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::stringstream ret;
    for (const unsigned char c : str) {
        if (c <= 32 || c >= 128 || c == '%') {
            ret << '%' << HexStr(&c, &c + 1);
        } else {
            ret << c;
        }
    }
    return ret.str();
}
static std::string DecodeDumpString(const std::string &str) {
    std::stringstream ret;
    for (unsigned int pos = 0; pos < str.length(); pos++) {
        unsigned char c = str[pos];
        if (c == '%' && pos+2 < str.length()) {
            c = (((str[pos+1]>>6)*9+((str[pos+1]-'0')&15)) << 4) |
                ((str[pos+2]>>6)*9+((str[pos+2]-'0')&15));
            pos += 2;
        }
        ret << c;
    }
    return ret.str();
}
static bool GetWalletAddressesForKey(CWallet * const pwallet, const CKeyID &keyid, std::string &strAddr, std::string &strLabel)