Does Confd provide any callback to intercept rpc attributes (eg: message-id or any custom attribute) sent via netconf rpc request?

NETCONF
2

Very limited. You can subscribe to CONFD_NOTIF_NETCONF events and your subscriber would get data structured according to

struct confd_syslog_notification {
    int prio;   /* from syslog.h */
    int logno;  /* number from confd_logsyms.h */
    char msg[BUFSIZ];
}

where some of what you ask for is in the message field. See the misc/notification example: do make START_FLAGS=-N all start, run NETCONF requests and watch the output to see if there is what you need.