At a minimum, help text should note this. This is true for things like addwitnessaddress especially.
"The command will pay the additional fee by decreasing (or perhaps removing) its change output.\n"
            "If the change output is not big enough to cover the increased fee, the command will currently fail\n"
            "instead of adding new inputs to compensate. (A future implementation could improve this.)\n"
            "The command will fail if the wallet or mempool contains a transaction that spends one of T's outputs.\n"
            "By default, the new fee will be calculated automatically using estimatefee.\n"
            "The user can specify a confirmation target for estimatefee.\n"
            "Alternatively, the user can specify totalFee, or use RPC settxfee to set a higher fee rate.\n"
            "At a minimum, the new fee rate must be high enough to pay an additional new relay fee (incrementalfee\n"
            "returned by getnetworkinfo) to enter the node's mempool.\n"
            "\nArguments:\n"
            "1. txid                  (string, required) The txid to be bumped\n"
            "2. options               (object, optional)\n"
            "   {\n"
            "     \"confTarget\"        (numeric, optional) Confirmation target (in blocks)\n"
            "     \"totalFee\"          (numeric, optional) Total fee (NOT feerate) to pay, in satoshis.\n"
            "                         In rare cases, the actual fee paid might be slightly higher than the specified\n"
            "                         totalFee if the tx change output has to be removed because it is too close to\n"
            "                         the dust threshold.\n"
            "     \"replaceable\"       (boolean, optional, default true) Whether the new transaction should still be\n"
            "                         marked bip-125 replaceable. If true, the sequence numbers in the transaction will\n"
            "                         be left unchanged from the original. If false, any input sequence numbers in the\n"
            "                         original transaction that were less than 0xfffffffe will be increased to 0xfffffffe\n"
            "                         so the new transaction will not be explicitly bip-125 replaceable (though it may\n"
            "                         still be replaceable in practice, for example if it has unconfirmed ancestors which\n"
            "                         are replaceable).\n"
            "     \"estimate_mode\"     (string, optional, default=UNSET) The fee estimate mode, must be one of:\n"
            "         \"UNSET\"\n"
            "         \"ECONOMICAL\"\n"
            "         \"CONSERVATIVE\"\n"
            "   }\n"