har -r archive-name [object-file...]
You can replace members in an archive using the -r switch. If you specify a file to add to the archive, and the archive doesn't contain that member already, the file is appended to the archive as a new member.
To replace the member ir.hzo in the archive cclib.hza with the file ir.hzo on disk, you would use:
har cclib.hza -r ir.hzo