How do you free the message ID returned by AR_DEFINE_MSG?
Once you've defined a message using AR_DEFINE_MSG, the unique message ID returned remains valid until AR_INIT_DUAL_PORT, AR_RESET, or AR_CLOSE is called. A scheduled transmission can be disabled by setting its rate to 0 with AR_MODIFY_MSG. The message may be enabled later by setting the rate to a non-zero value.
A maximum of 120 scheduled messages per channel are supported on the CEI-x20.