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")
```

ssMB >> merkleBlock;
    
    std::vector<uint256> vMatch;
    std::vector<unsigned int> vIndex;
    unsigned int txnIndex = 0;
    if (merkleBlock.txn.ExtractMatches(vMatch, vIndex) == merkleBlock.header.hashMerkleRoot) {
        LOCK(cs_main);
        const CBlockIndex* pindex = LookupBlockIndex(merkleBlock.header.GetHash());
        if (!pindex || !chainActive.Contains(pindex)) {
            throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Block not found in chain");
        }
        std::vector<uint256>::const_iterator it;
        if ((it = std::find(vMatch.begin(), vMatch.end(), hashTx))==vMatch.end()) {
            throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Transaction given doesn't exist in proof");
        }
        txnIndex = vIndex[it - vMatch.begin()];
    }
    else {
        throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Something wrong with merkleblock");
    }
    wtx.nIndex = txnIndex;
    wtx.hashBlock = merkleBlock.header.GetHash();
    LOCK2(cs_main, pwallet->cs_wallet);
    if (pwallet->IsMine(*wtx.tx)) {
        pwallet->AddToWallet(wtx, false);
        return NullUniValue;
    }
    throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "No addresses in wallet correspond to included transaction");
}
UniValue removeprunedfunds(const JSONRPCRequest& request)