Current behavior:

• Neither in shared project nor shared job scenario, it is not possible to prevent Vendor's Admin or PM from editing already Completed jobs.

 
Requested behavior:

• In shared projects and jobs, it is possible to prevent Vendor's Admin or PM from editing already Completed jobs.

 
Workaround:

• With shared project: Unshare the project
• With shared jobs: Unassign the vendor from the job

 
Use case:

• Even though the job is set as Completed, there is still a high risk of undetected and unwanted changes being introduced at the behest of the Vendor.