It sure sucks if you have multiple apps using the crontab and you go to add your new task to the crontab using whenever -w and it overwrites all of your other rules.

They have a helpful option that aids with this. It handles multiple apps or tasks

whenever --update-crontab some_identifier

Now whenever you want to overwrite that rule use the same identifier.
If you want a new rule then use a new identifier.

Related External Links:

• Stack Overflow - can-the-whenever-gem-preserve-existing-lines-in-a-crontab-file