Yes, this can be done by removing the existing Reviewer email from the program and by entering a new Reviewer email address in its place. 

This change can be made after the assessment has been targeted. The new Reviewer will not receive an additional email notification; however, they will see the assessments listed as In Review within their 'Privacy Reviews' tile.

Please note that it is not possible to change the Reviewer per assessment; you can only change the Reviewer per program.