At a minimum, help text should note this. This is true for things like addwitnessaddress especially.
if (options.exists("subtractFeeFromOutputs"))
            subtractFeeFromOutputs = options["subtractFeeFromOutputs"].get_array();
        if (options.exists("replaceable")) {
            coinControl.signalRbf = options["replaceable"].get_bool();
        }
        if (options.exists("conf_target")) {
            if (options.exists("feeRate")) {
                throw JSONRPCError(RPC_INVALID_PARAMETER, "Cannot specify both conf_target and feeRate");
            }
            coinControl.m_confirm_target = ParseConfirmTarget(options["conf_target"]);
        }
        if (options.exists("estimate_mode")) {
            if (options.exists("feeRate")) {
                throw JSONRPCError(RPC_INVALID_PARAMETER, "Cannot specify both estimate_mode and feeRate");
            }
            if (!FeeModeFromString(options["estimate_mode"].get_str(), coinControl.m_fee_mode)) {
                throw JSONRPCError(RPC_INVALID_PARAMETER, "Invalid estimate_mode parameter");
            }
        }
      }
    }
    
    CMutableTransaction tx;
    if (!DecodeHexTx(tx, request.params[0].get_str(), true))
        throw JSONRPCError(RPC_DESERIALIZATION_ERROR, "TX decode failed");
    if (tx.vout.size() == 0)
        throw JSONRPCError(RPC_INVALID_PARAMETER, "TX must have at least one output");
    if (changePosition != -1 && (changePosition < 0 || (unsigned int)changePosition > tx.vout.size()))
        throw JSONRPCError(RPC_INVALID_PARAMETER, "changePosition out of bounds");
    for (unsigned int idx = 0; idx < subtractFeeFromOutputs.size(); idx++) {