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.
RPCHelpMan psbtbumpfee() { return bumpfee_helper("psbtbumpfee"); }
RPCHelpMan send()
{
    return RPCHelpMan{"send",
        "\nEXPERIMENTAL warning: this call may be changed in future releases.\n"
        "\nSend a transaction.\n",
        {
            {"outputs", RPCArg::Type::ARR, RPCArg::Optional::NO, "The outputs (key-value pairs), where none of the keys are duplicated.\n"
                    "That is, each address can only appear once and there can only be one 'data' object.\n"
                    "For convenience, a dictionary, which holds the key-value pairs directly, is also accepted.",
                OutputsDoc(),
                RPCArgOptions{.skip_type_check = true}},
            {"conf_target", RPCArg::Type::NUM, RPCArg::DefaultHint{"wallet -txconfirmtarget"}, "Confirmation target in blocks"},
            {"estimate_mode", RPCArg::Type::STR, RPCArg::Default{"unset"}, "The fee estimate mode, must be one of (case insensitive):\n"
             "\"" + FeeModes("\"\n\"") + "\""},
            {"fee_rate", RPCArg::Type::AMOUNT, RPCArg::DefaultHint{"not set, fall back to wallet fee estimation"}, "Specify a fee rate in " + CURRENCY_ATOM + "/vB."},
            {"options", RPCArg::Type::OBJ_NAMED_PARAMS, RPCArg::Optional::OMITTED, "",
                Cat<std::vector<RPCArg>>(
                {
                    {"add_inputs", RPCArg::Type::BOOL, RPCArg::DefaultHint{"false when \"inputs\" are specified, true otherwise"},"Automatically include coins from the wallet to cover the target amount.\n"},
                    {"include_unsafe", RPCArg::Type::BOOL, RPCArg::Default{false}, "Include inputs that are not safe to spend (unconfirmed transactions from outside keys and unconfirmed replacement transactions).\n"
                                                          "Warning: the resulting transaction may become invalid if one of the unsafe inputs disappears.\n"
                                                          "If that happens, you will need to fund the transaction with different inputs and republish it."},
                    {"minconf", RPCArg::Type::NUM, RPCArg::Default{0}, "If add_inputs is specified, require inputs with at least this many confirmations."},
                    {"maxconf", RPCArg::Type::NUM, RPCArg::Optional::OMITTED, "If add_inputs is specified, require inputs with at most this many confirmations."},
                    {"add_to_wallet", RPCArg::Type::BOOL, RPCArg::Default{true}, "When false, returns a serialized transaction which will not be added to the wallet or broadcast"},
                    {"change_address", RPCArg::Type::STR, RPCArg::DefaultHint{"automatic"}, "The bitcoin address to receive the change"},
                    {"change_position", RPCArg::Type::NUM, RPCArg::DefaultHint{"random"}, "The index of the change output"},