### 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_
{ "addmultisigaddress", 1, "keys" },
    { "createmultisig", 0, "nrequired" },
    { "createmultisig", 1, "keys" },
    { "listunspent", 0, "minconf" },
    { "listunspent", 1, "maxconf" },
    { "listunspent", 2, "addresses" },
    { "listunspent", 3, "include_unsafe" },
    { "listunspent", 4, "query_options" },
    { "listunspent", 4, "minimumAmount" },
    { "listunspent", 4, "maximumAmount" },
    { "listunspent", 4, "maximumCount" },
    { "listunspent", 4, "minimumSumAmount" },
    { "listunspent", 4, "include_immature_coinbase" },
    { "getblock", 1, "verbosity" },
    { "getblock", 1, "verbose" },
    { "getblockheader", 1, "verbose" },
    { "getchaintxstats", 0, "nblocks" },
    { "gettransaction", 1, "include_watchonly" },
    { "gettransaction", 2, "verbose" },
    { "getrawtransaction", 1, "verbosity" },
    { "getrawtransaction", 1, "verbose" },
    { "createrawtransaction", 0, "inputs" },
    { "createrawtransaction", 1, "outputs" },
    { "createrawtransaction", 2, "locktime" },
    { "createrawtransaction", 3, "replaceable" },
    { "decoderawtransaction", 1, "iswitness" },
    { "signrawtransactionwithkey", 1, "privkeys" },
    { "signrawtransactionwithkey", 2, "prevtxs" },
    { "signrawtransactionwithwallet", 1, "prevtxs" },
    { "sendrawtransaction", 1, "maxfeerate" },