Restarting cron after changing crontab file? [closed]

Do I have to restart cron after changing the crontable file?

No.

From the cron man page:

…cron will then examine the modification time on all crontabs
and reload those which have changed. Thus cron need not be restarted
whenever a crontab file is modified

But if you just want to make sure its done anyway,

sudo service cron reload

or

/etc/init.d/cron reload