### 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_
{ "generatetoaddress", 2, "maxtries" },
    { "generatetodescriptor", 0, "num_blocks" },
    { "generatetodescriptor", 2, "maxtries" },
    { "generateblock", 1, "transactions" },
    { "generateblock", 2, "submit" },
    { "getnetworkhashps", 0, "nblocks" },
    { "getnetworkhashps", 1, "height" },
    { "sendtoaddress", 1, "amount" },
    { "sendtoaddress", 4, "subtractfeefromamount" },
    { "sendtoaddress", 5 , "replaceable" },
    { "sendtoaddress", 6 , "conf_target" },
    { "sendtoaddress", 8, "avoid_reuse" },
    { "sendtoaddress", 9, "fee_rate"},
    { "sendtoaddress", 10, "verbose"},
    { "settxfee", 0, "amount" },
    { "sethdseed", 0, "newkeypool" },
    { "getreceivedbyaddress", 1, "minconf" },
    { "getreceivedbyaddress", 2, "include_immature_coinbase" },
    { "getreceivedbylabel", 1, "minconf" },
    { "getreceivedbylabel", 2, "include_immature_coinbase" },
    { "listreceivedbyaddress", 0, "minconf" },
    { "listreceivedbyaddress", 1, "include_empty" },
    { "listreceivedbyaddress", 2, "include_watchonly" },
    { "listreceivedbyaddress", 4, "include_immature_coinbase" },
    { "listreceivedbylabel", 0, "minconf" },
    { "listreceivedbylabel", 1, "include_empty" },
    { "listreceivedbylabel", 2, "include_watchonly" },
    { "listreceivedbylabel", 3, "include_immature_coinbase" },
    { "getbalance", 1, "minconf" },
    { "getbalance", 2, "include_watchonly" },