# min hh24  dd mm weekday  cmd
05  22  *  *  1,2,3,4,5  /home/user/bin/myjob.sh
04  22  18  02  *         /bin/crontab -l | grep -v |  /home/user/bin/myjob.sh | /bin/crontab 

$ crontab -l
#
04 22 * * 1,2,3,4,5  /home/mytest.sh
00 22 18 02 * /bin/crontab -l | grep -v /home/mytest.sh | /bin/crontab 
$  /bin/crontab -l | grep -v /home/mytest.sh
#
$ /bin/crontab -l | grep -v /home/mytest.sh | /bin/crontab 
$ crontab -l
#

$ cat crongen.sh 
#!/bin/sh
cmd=/bin/crontab

# test output
T=echo  
cmd="cat -"

#  now
mon=`date +%m`
day=`date +%d`

# calculate
case $mon in
01|02|03|04|05|06)
		mon=`expr $mon + 6`
		;;
07|08|09|10|11|12)
		mon=`expr $mon - 6`
		;;
*)
	mon=99
esac

export mon day

# make new crontab
(
$T crontab -l
echo "04 22 * * 1,2,3,4,5  /home/mytest.sh"
echo "00 22 $day $mon * /bin/crontab -l | grep -v /home/mytest.sh | /bin/crontab"
) | $cmd