### 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_
{ "sendrawtransaction", 2, "maxburnamount" },
    { "testmempoolaccept", 0, "rawtxs" },
    { "testmempoolaccept", 1, "maxfeerate" },
    { "submitpackage", 0, "package" },
    { "combinerawtransaction", 0, "txs" },
    { "fundrawtransaction", 1, "options" },
    { "fundrawtransaction", 1, "add_inputs"},
    { "fundrawtransaction", 1, "include_unsafe"},
    { "fundrawtransaction", 1, "minconf"},
    { "fundrawtransaction", 1, "maxconf"},
    { "fundrawtransaction", 1, "changePosition"},
    { "fundrawtransaction", 1, "includeWatching"},
    { "fundrawtransaction", 1, "lockUnspents"},
    { "fundrawtransaction", 1, "fee_rate"},
    { "fundrawtransaction", 1, "feeRate"},
    { "fundrawtransaction", 1, "subtractFeeFromOutputs"},
    { "fundrawtransaction", 1, "input_weights"},
    { "fundrawtransaction", 1, "conf_target"},
    { "fundrawtransaction", 1, "replaceable"},
    { "fundrawtransaction", 1, "solving_data"},
    { "fundrawtransaction", 2, "iswitness" },
    { "walletcreatefundedpsbt", 0, "inputs" },
    { "walletcreatefundedpsbt", 1, "outputs" },
    { "walletcreatefundedpsbt", 2, "locktime" },
    { "walletcreatefundedpsbt", 3, "options" },
    { "walletcreatefundedpsbt", 3, "add_inputs"},
    { "walletcreatefundedpsbt", 3, "include_unsafe"},
    { "walletcreatefundedpsbt", 3, "minconf"},
    { "walletcreatefundedpsbt", 3, "maxconf"},
    { "walletcreatefundedpsbt", 3, "changePosition"},