Can I edit which Worker Groups I source from on individual Shifts?

Yes, as long as you haven't published the Shift yet, you can update the sourcing options at the Shift level.

You can customize the sourcing options at the individual Shift level. This will only apply to future Shifts you post. If your Shift is already published, you cannot remove any existing Worker Groups. You can always add more groups to source from, but you cannot remove them.

If you would like to learn more about Worker Groups, please see this blog post.