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("conf_target") || options.exists("estimate_mode")) {
        if (!conf_target.isNull() || !estimate_mode.isNull()) {
            throw JSONRPCError(RPC_INVALID_PARAMETER, "Pass conf_target and estimate_mode either as arguments or in the options object, but not both");
        }
    } else {
        options.pushKV("conf_target", conf_target);
        options.pushKV("estimate_mode", estimate_mode);
    }
    if (options.exists("fee_rate")) {
        if (!fee_rate.isNull()) {
            throw JSONRPCError(RPC_INVALID_PARAMETER, "Pass the fee_rate either as an argument, or in the options object, but not both");
        }
    } else {
        options.pushKV("fee_rate", fee_rate);
    }
    if (!options["conf_target"].isNull() && (options["estimate_mode"].isNull() || (options["estimate_mode"].get_str() == "unset"))) {
        throw JSONRPCError(RPC_INVALID_PARAMETER, "Specify estimate_mode");
    }
}
static UniValue FinishTransaction(const std::shared_ptr<CWallet> pwallet, const UniValue& options, const CMutableTransaction& rawTx)
{
    
    PartiallySignedTransaction psbtx(rawTx);
    
    
    bool complete;