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 (wallet.chain().hasDescendantsInMempool(wtx.GetHash())) {
            errors.push_back(Untranslated("Transaction has descendants in the mempool"));
            return feebumper::Result::INVALID_PARAMETER;
        }
    }
    if (wallet.GetTxDepthInMainChain(wtx) != 0) {
        errors.push_back(Untranslated("Transaction has been mined, or is conflicted with a mined transaction"));
        return feebumper::Result::WALLET_ERROR;
    }
    if (!SignalsOptInRBF(*wtx.tx)) {
        errors.push_back(Untranslated("Transaction is not BIP 125 replaceable"));
        return feebumper::Result::WALLET_ERROR;
    }
    if (wtx.mapValue.count("replaced_by_txid")) {
        errors.push_back(strprintf(Untranslated("Cannot bump transaction %s which was already bumped by transaction %s"), wtx.GetHash().ToString(), wtx.mapValue.at("replaced_by_txid")));
        return feebumper::Result::WALLET_ERROR;
    }
    if (require_mine) {
        
        
        isminefilter filter = wallet.GetLegacyScriptPubKeyMan() && wallet.IsWalletFlagSet(WALLET_FLAG_DISABLE_PRIVATE_KEYS) ? ISMINE_WATCH_ONLY : ISMINE_SPENDABLE;
        if (!AllInputsMine(wallet, *wtx.tx, filter)) {
            errors.push_back(Untranslated("Transaction contains inputs that don't belong to this wallet"));
            return feebumper::Result::WALLET_ERROR;
        }
    }
    return feebumper::Result::OK;
}
static feebumper::Result CheckFeeRate(const CWallet& wallet, const CFeeRate& newFeerate, const int64_t maxTxSize, CAmount old_fee, std::vector<bilingual_str>& errors)