Load balancing ISPs on Ubuntu Server

I believe the script you found was created by following/amalgamating the various pieces of information from the Linux Advanced Routing & Traffic Control HOWTO. Specifically the section on load balancing separate ISP links. I suggest you read that page to help understand what that script is doing. Keep in mind that that How To references old Kernels though I don't think the principle would have changed much and the ip commands are probably still valid.

That script would need to be run each time the machine boots to set the routes etc. so you don't need to backup files (it doesn't touch any). Once you reboot the machine the rules will be forgotten and the machine's default network setup will be used.

If you don't want to reboot then, depending on the distro, you may be able to restart the networking i.e. on Red Hat a service network restart should clear the routes for you and add the default route again (this is based on my quick scan of the network scripts). I believe Ubuntu will have a similar system (I haven't used it for some time and they use Upstart nowadays which I have no knowledge of). Otherwise you'd have to manually remove the rules that that script creates (or write a script that does it) using the ip command.