### 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_
{
    std::set<CTxDestination> destinations;
    int i = 0;
    for (const std::string& address: address_amounts.getKeys()) {
        CTxDestination dest = DecodeDestination(address);
        if (!IsValidDestination(dest)) {
            throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, std::string("Invalid Bitcoin address: ") + address);
        }
        if (destinations.count(dest)) {
            throw JSONRPCError(RPC_INVALID_PARAMETER, std::string("Invalid parameter, duplicated address: ") + address);
        }
        destinations.insert(dest);
        CAmount amount = AmountFromValue(address_amounts[i++]);
        bool subtract_fee = false;
        for (unsigned int idx = 0; idx < subtract_fee_outputs.size(); idx++) {
            const UniValue& addr = subtract_fee_outputs[idx];
            if (addr.get_str() == address) {
                subtract_fee = true;
            }
        }
        CRecipient recipient = {dest, amount, subtract_fee};
        recipients.push_back(recipient);
    }
}
static void InterpretFeeEstimationInstructions(const UniValue& conf_target, const UniValue& estimate_mode, const UniValue& fee_rate, UniValue& options)