If I create an RBF transaction using the Qt GUI but specify my own custom change address, bumpfee doesn't work because it claims it can't find the change address:

    "Transaction does not have a change output"

This is because none of the outputs satisfy

    pWallet->IsChange(...)

I see there's a "TODO" commented in `CWallet::IsChange()` in `src/wallet/wallet.cpp`:

    // TODO: fix handling of 'change' outputs. The assumption is that any
    // payment to a script that is ours, but is not in the address book
    // is change.

I tend to put all my addresses in the address book whether I'm going to use them as change or not. I guess if the wallet was capable of creating its own SegWit change addresses I'd stop using custom change addresses, but currently it always seems to send change to a legacy address if I don't manually specify a change address.
RPCArgOptions{.oneline_description="options"}},
        },
        RPCResult{
            RPCResult::Type::OBJ, "", "",
                {
                    {RPCResult::Type::BOOL, "complete", "If the transaction has a complete set of signatures"},
                    {RPCResult::Type::STR_HEX, "txid", true, "The transaction id for the send. Only 1 transaction is created regardless of the number of addresses."},
                    {RPCResult::Type::STR_HEX, "hex", true, "If add_to_wallet is false, the hex-encoded raw transaction with signature(s)"},
                    {RPCResult::Type::STR, "psbt", true, "If more signatures are needed, or if add_to_wallet is false, the base64-encoded (partially) signed transaction"}
                }
        },
        RPCExamples{""
        "\nSend 0.1 BTC with a confirmation target of 6 blocks in economical fee estimate mode\n"
        + HelpExampleCli("send", "'{\"" + EXAMPLE_ADDRESS[0] + "\": 0.1}' 6 economical\n") +
        "Send 0.2 BTC with a fee rate of 1.1 " + CURRENCY_ATOM + "/vB using positional arguments\n"
        + HelpExampleCli("send", "'{\"" + EXAMPLE_ADDRESS[0] + "\": 0.2}' null \"unset\" 1.1\n") +
        "Send 0.2 BTC with a fee rate of 1 " + CURRENCY_ATOM + "/vB using the options argument\n"
        + HelpExampleCli("send", "'{\"" + EXAMPLE_ADDRESS[0] + "\": 0.2}' null \"unset\" null '{\"fee_rate\": 1}'\n") +
        "Send 0.3 BTC with a fee rate of 25 " + CURRENCY_ATOM + "/vB using named arguments\n"
        + HelpExampleCli("-named send", "outputs='{\"" + EXAMPLE_ADDRESS[0] + "\": 0.3}' fee_rate=25\n") +
        "Create a transaction that should confirm the next block, with a specific input, and return result without adding to wallet or broadcasting to the network\n"
        + HelpExampleCli("send", "'{\"" + EXAMPLE_ADDRESS[0] + "\": 0.1}' 1 economical '{\"add_to_wallet\": false, \"inputs\": [{\"txid\":\"a08e6907dbbd3d809776dbfc5d82e371b764ed838b5655e72f463568df1aadf0\", \"vout\":1}]}'")
        },
        [&](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue
        {
            std::shared_ptr<CWallet> const pwallet = GetWalletForJSONRPCRequest(request);
            if (!pwallet) return UniValue::VNULL;
            UniValue options{request.params[4].isNull() ? UniValue::VOBJ : request.params[4]};
            InterpretFeeEstimationInstructions(request.params[1], request.params[2], request.params[3], options);
            PreventOutdatedOptions(options);