How can we add or delete shift tags/project tasks in Workday?

You can unassign the shift tags from Humanity; however, there will be no impact on Workday.

If you unassign shift tags from employee's profile in Workday it will sync with Humanity. However, if you unassign the shifts tags within humanity employee's profile, It will not sync back to Workday.

Account related shifts tags will only be made through API.