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.
},
                        },
                        FundTxDoc()),
                        RPCArgOptions{.oneline_description="options"}},
                    {"bip32derivs", RPCArg::Type::BOOL, RPCArg::Default{true}, "Include BIP 32 derivation paths for public keys if we know them"},
                },
                RPCResult{
                    RPCResult::Type::OBJ, "", "",
                    {
                        {RPCResult::Type::STR, "psbt", "The resulting raw transaction (base64-encoded string)"},
                        {RPCResult::Type::STR_AMOUNT, "fee", "Fee in " + CURRENCY_UNIT + " the resulting transaction pays"},
                        {RPCResult::Type::NUM, "changepos", "The position of the added change output, or -1"},
                    }
                                },
                                RPCExamples{
                            "\nCreate a transaction with no inputs\n"
                            + HelpExampleCli("walletcreatefundedpsbt", "\"[{\\\"txid\\\":\\\"myid\\\",\\\"vout\\\":0}]\" \"[{\\\"data\\\":\\\"00010203\\\"}]\"")
                                },
        [&](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue
{
    std::shared_ptr<CWallet> const pwallet = GetWalletForJSONRPCRequest(request);
    if (!pwallet) return UniValue::VNULL;
    CWallet& wallet{*pwallet};
    
    
    wallet.BlockUntilSyncedToCurrentChain();
    UniValue options{request.params[3].isNull() ? UniValue::VOBJ : request.params[3]};
    CAmount fee;
    int change_position;
    const UniValue &replaceable_arg = options["replaceable"];