You need to deactived (change) this variable in the CTRL Start menu
Some of the variables is protected when you try to change them in normal start, and only way how to change them is in the CTRL Start menu....that´s all...
If you have R30iB Mate controller press FCTN button → next→ Cycle power → Options → CTRL and you need to restart the controller
Then CTRL start is started and you are able to change variables