Life after death on a project by project basis - project locking

I would like the ability to manually lock a project from additional updates on a project by project basis.

We need the ability to add time and supporting documents to a project for a period of time after the Project Manager "completes" the project. But want to lock it from additional updates after a desired period of time (say 2 weeks).

Currently, it is locked at status completion or not at all.