Hi,
Yes, it is possible, but periodic reboot can only do one thing per this configuration - it's either a normal router reboot, or a modem reboot.
So I would suggest you do two configurations - Ping reboot and Period reboot.
Set your ping reboot to restart a modem once your ping stops going through and set periodic reboot for your router to reboot it weekly, this way you will only reboot your modem when you lose the connection, and the router will just reboot once in a week.
You can find more about this kind of configuration here
EB.