How can I make Signal Builder output a signal repeatedly, i.e. infinitely?

I'm trying to use Signal Builder to generate a custom signal repeatedly--infinitely until I stop execution of the simulation. I can't find anything in the documentation, and setting the time limit to inf results in an error.

I was going to try to edit Signal Builder, putting in a trigger that would restart the block upon a second signal from the block going high, but the right-click menu option to undo the link to the library as well as the entry to look under the mask are both greyed out so I can't edit it.

Any suggestions?