Is there a way to add a service such as 'ping' to multiple devices at once? I would like to add a new service to some of my existing routers in the Dude, but the thought of manually clicking each router individually doesn't sound too appealing...

From what I can tell, the dude doesn't support this under the Services tab but would it be possible to do this via a script?

any luck on this? after a restore from backup all my devices have lost the ping service.

Only if you have these devices under the same network map, where you can select auto-discovery for specific services.