Even though your Policy has already been published, you can still add new users to the target list.  

1. Find the required Policy under Products>Policy>Policies In Progress. 
2. Under the Actions column, select Options>View Policy.
3. Select the Target tab.
4. Locate, and select the new users you require to be targeted.
5. Click Update Targets.
6. You will receive a validation message outlining the total number of users you are about to target; if this is correct, then select Confirm, and the new users will be targeted.