### 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("changePosition") || options.exists("change_position")) {
            change_position = (options.exists("change_position") ? options["change_position"] : options["changePosition"]).getInt<int>();
        }
        if (options.exists("change_type")) {
            if (options.exists("changeAddress") || options.exists("change_address")) {
                throw JSONRPCError(RPC_INVALID_PARAMETER, "Cannot specify both change address and address type options");
            }
            if (std::optional<OutputType> parsed = ParseOutputType(options["change_type"].get_str())) {
                coinControl.m_change_type.emplace(parsed.value());
            } else {
                throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, strprintf("Unknown change type '%s'", options["change_type"].get_str()));
            }
        }
        const UniValue include_watching_option = options.exists("include_watching") ? options["include_watching"] : options["includeWatching"];
        coinControl.fAllowWatchOnly = ParseIncludeWatchonly(include_watching_option, wallet);
        if (options.exists("lockUnspents") || options.exists("lock_unspents")) {
            lockUnspents = (options.exists("lock_unspents") ? options["lock_unspents"] : options["lockUnspents"]).get_bool();
        }
        if (options.exists("include_unsafe")) {
            coinControl.m_include_unsafe_inputs = options["include_unsafe"].get_bool();
        }
        if (options.exists("feeRate")) {
            if (options.exists("fee_rate")) {
                throw JSONRPCError(RPC_INVALID_PARAMETER, "Cannot specify both fee_rate (" + CURRENCY_ATOM + "/vB) and feeRate (" + CURRENCY_UNIT + "/kvB)");
            }
            if (options.exists("conf_target")) {
                throw JSONRPCError(RPC_INVALID_PARAMETER, "Cannot specify both conf_target and feeRate. Please provide either a confirmation target in blocks for automatic fee estimation, or an explicit fee rate.");
            }
            if (options.exists("estimate_mode")) {