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.
if (options.exists("minconf")) {
                if (options["minconf"].getInt<int>() < 0)
                {
                    throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("Invalid minconf (minconf cannot be negative): %s", options["minconf"].getInt<int>()));
                }
                coin_control.m_min_depth = options["minconf"].getInt<int>();
            }
            if (options.exists("maxconf")) {
                coin_control.m_max_depth = options["maxconf"].getInt<int>();
                if (coin_control.m_max_depth < coin_control.m_min_depth) {
                    throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("maxconf can't be lower than minconf: %d < %d", coin_control.m_max_depth, coin_control.m_min_depth));
                }
            }
            const bool rbf{options.exists("replaceable") ? options["replaceable"].get_bool() : pwallet->m_signal_rbf};
            FeeCalculation fee_calc_out;
            CFeeRate fee_rate{GetMinimumFeeRate(*pwallet, coin_control, &fee_calc_out)};
            /
            /
            if (coin_control.m_feerate && fee_rate > *coin_control.m_feerate) {
               throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("Fee rate (%s) is lower than the minimum fee rate setting (%s)", coin_control.m_feerate->ToString(FeeEstimateMode::SAT_VB), fee_rate.ToString(FeeEstimateMode::SAT_VB)));
            }
            if (fee_calc_out.reason == FeeReason::FALLBACK && !pwallet->m_allow_fallback_fee) {
                /
                throw JSONRPCError(RPC_WALLET_ERROR, "Fee estimation failed. Fallbackfee is disabled. Wait a few blocks or enable -fallbackfee.");
            }
            CMutableTransaction rawTx{ConstructTransaction(options["inputs"], recipient_key_value_pairs, options["locktime"], rbf)};
            LOCK(pwallet->cs_wallet);
            CAmount total_input_value(0);
            bool send_max{options.exists("send_max") ? options["send_max"].get_bool() : false};
            if (options.exists("inputs") && options.exists("send_max")) {