### 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_
{
    if (options.exists("conf_target") || options.exists("estimate_mode")) {
        if (!conf_target.isNull() || !estimate_mode.isNull()) {
            throw JSONRPCError(RPC_INVALID_PARAMETER, "Pass conf_target and estimate_mode either as arguments or in the options object, but not both");
        }
    } else {
        options.pushKV("conf_target", conf_target);
        options.pushKV("estimate_mode", estimate_mode);
    }
    if (options.exists("fee_rate")) {
        if (!fee_rate.isNull()) {
            throw JSONRPCError(RPC_INVALID_PARAMETER, "Pass the fee_rate either as an argument, or in the options object, but not both");
        }
    } else {
        options.pushKV("fee_rate", fee_rate);
    }
    if (!options["conf_target"].isNull() && (options["estimate_mode"].isNull() || (options["estimate_mode"].get_str() == "unset"))) {
        throw JSONRPCError(RPC_INVALID_PARAMETER, "Specify estimate_mode");
    }
}
static UniValue FinishTransaction(const std::shared_ptr<CWallet> pwallet, const UniValue& options, const CMutableTransaction& rawTx)
{
    
    PartiallySignedTransaction psbtx(rawTx);
    
    
    bool complete;