[I discourage rebooting (or worse, power cycling) of any device with intelligence, memory, and communication, without good reason. It is a form of oppression, abuse (and possibly violence) that diminishes the intelligence of both victim and perpetrator.]
What ISP problem exiists, and why did someone think it necessitates rebooting the modem (and the router)?
The curl invocation simply opens a web page on the modem and checks "Reset Request" on the form.
(You can do the same interactively by feeding the URL to your browser.)
(Curl is a tool for automating what would otherwise be interactive sessions with various servers, including HTTP.)
Curl is not included with Tomato distributions, but it can easily be put on a Tomato router.
So, this curl script could be run from a Custom script in the Scheduler, which also has a predefined script for Rebooting the router. —- Administration > Scheduler
It is almost certainly possible to access the modem via telnet, in which case curl is unnecessary.
But, depending on what that "ISP problem" really is, perhaps all that is necessary (and appropriate), is to get a new WAN IP. That can be scheduled with a predefined box in the Scheduler: [Reconnect]. I would simply try that and see if it solves the problem.
Before setting up the Scheduler I would suggest:
On the Overview page, [Disconnect] the WAN, and then [Reconnect].
See if that solves the problem.