### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current behaviour

See inline discussion at https://github.com/bitcoin/bitcoin/pull/26467#discussion_r1269177446

@whitslack:

> Consider the case where I am paying someone on chain under the stipulation that _they_ will eat the mining fee. (Thus, I specify _their_ address in `subtractfeefrom` when I'm constructing my transaction.) Later, they tell me that they can't wait for confirmation any longer and need an urgent fee bump. If I naïvely specify their output as the `reduce_output`, I may end up paying them _**much more**_ than I intended to if I only have large UTxOs in my wallet.


### Expected behaviour

Not sure.

Improving the docs is one option, but this behaviour seem quite counter intuitive.

My own suggestion:

> Should we disable the adding of new inputs when `reduce_output` is set? If someone really intends to do that, they should probably use `outputs`.

### Steps to reproduce

Haven't tried.

### Relevant log output

_No response_

### How did you obtain Bitcoin Core

Compiled from source

### What version of Bitcoin Core are you using?

Master after #26467

### Operating system and version

Any

### Machine specifications

_No response_
{
    LOCK(wallet.cs_wallet);
    const CWalletTx* wtx = wallet.GetWalletTx(txid);
    if (wtx == nullptr) return false;
    std::vector<bilingual_str> errors_dummy;
    feebumper::Result res = PreconditionChecks(wallet, *wtx,  true, errors_dummy);
    return res == feebumper::Result::OK;
}
Result CreateRateBumpTransaction(CWallet& wallet, const uint256& txid, const CCoinControl& coin_control, std::vector<bilingual_str>& errors,
                                 CAmount& old_fee, CAmount& new_fee, CMutableTransaction& mtx, bool require_mine, const std::vector<CTxOut>& outputs, std::optional<uint32_t> reduce_output)
{
    
    if (!outputs.empty() && reduce_output.has_value()) {
        errors.push_back(Untranslated("Cannot specify both new outputs to use and an output index to reduce"));
        return Result::INVALID_PARAMETER;
    }
    
    CCoinControl new_coin_control(coin_control);
    LOCK(wallet.cs_wallet);
    errors.clear();
    auto it = wallet.mapWallet.find(txid);
    if (it == wallet.mapWallet.end()) {
        errors.push_back(Untranslated("Invalid or non-wallet transaction id"));
        return Result::INVALID_ADDRESS_OR_KEY;
    }
    const CWalletTx& wtx = it->second;
    
    if (reduce_output.has_value() && reduce_output.value() >= wtx.tx->vout.size()) {
        errors.push_back(Untranslated("Change position is out of range"));
        return Result::INVALID_PARAMETER;