### 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_
{
        switch (sigversion) {
        case SigVersion::BASE:
            m_sigs_weight += weight * WITNESS_SCALE_FACTOR;
            m_sigs_count += 1 * WITNESS_SCALE_FACTOR;
            break;
        case SigVersion::WITNESS_V0:
            m_sigs_weight += weight;
            m_sigs_count++;
            break;
        case SigVersion::TAPROOT:
        case SigVersion::TAPSCRIPT:
            assert(false);
        }
    }
    int64_t GetWeightDiffToMax() const
    {
        
        return ( 72 * m_sigs_count) - m_sigs_weight;
    }
};
class SignatureWeightChecker : public DeferringSignatureChecker