Do I have to restart cron after changing the crontable file?
Depending on distribution, using "cron reload" might do nothing. To paste a snippet out of init.d/cron (debian squeeze):
reload|force-reload) log_daemon_msg "Reloading configuration files for periodic command scheduler" "cron"
# cron reloads automatically
log_end_msg 0
;;
Some developer/maintainer relied on it reloading, but doesn't, and in this case there's not a way to force reload. I'm generating my crontab files as part of a deploy, and unless somehow the length of the file changes, the changes are not reloaded.