Virtuoso / Skill: how to change access permissions to cells?

Dear all,
to avoid any changes to cells after a certain milestone, i want to remove the "write" attributes from the cells; this should be done by a script, not manually via the library-manager;

Is there a skill-function to achieve this? A ddSet...-equivalent of ddGetObjAccess seems not to exist;

System: virtuoso 6.1.3 on RHEL

When i do a "chmod a-w" on the terminal to the .oa-file of my layout-view, everything is fine, but when i'm calling "chmod  a-w ..." by a Skill-"system"-call, the cell gets locked and the lock is not released again. The .oa-file is changed, permissions are set as desired, but i can still open the cell in edit mode, it's just the other way round, virtuoso refuses to open it read-only and tells me it's already open in edit-mode.

Regarding file locking: when i'm opening a cell for editing, there are two lock-files generated, as expected mycellname.oa.cdslck and an additional file mycellname.cdslckRHEL....hostnameandsoon.
When the cellview is closed, both of them disappear.

After the chmod-system-call, these two files persist until virtuoso has been restarted.

clsAdminTool is not capable to release the lock, ddLockFree and associated commands fail too.

Any idea how to avoid the locking-problem and/or how to do the job of setting my cells to read-only by skill?
What about the concept itself, the cells need to be accessible but protected, adding cells to the library is required;
is this approach sufficiently safe?

kind regards, many thanks
Stefan