You cannot change parameters unless the "Parameter Write Enable" (PWE) bit is set. Fanuc 10M CNC Parameter Guide | PDF | Ascii - Scribd
These are the "SETTING" parameters, accessible via the [PARAM] key then the [SETTING] soft key. They control fundamental machine behavior: Fanuc 10m Parameter Manual
Defines the behavior of physical axes, including movement directions and grid shifts. You cannot change parameters unless the "Parameter Write