A school can mass update existing historical marks by navigating to Security > Update > Historical Marks.  You need the Security Full role to access this page.  

Note: The easiest way to use the update historical marks is to create a DAT report that includes Hist Student Mark Id, and other fields you want to update.  Export the data, make sure the column names match the Update column name and run the Update.

See also
Historical Mark    DAT   
PCR Educator K-12 School Information System is an online database engineered for independent and private schools to deliver the highest level of flexibility, unique experience, transparent communication and customized design. Being a complete cloud-based solution, PCR Educator system guarantees convenient access anytime, anywhere.