If the chip has subsequently been programmed to run from the XOSC then setting this field to DISABLE may lock-up the chip. If this is a concern then run the clk_ref from the ROSC and enable the clk_sys RESUS feature.
The 12-bit code is intended to give some protection against accidental writes. An invalid setting will enable the oscillator.
struct ENABLE_W<'a, REG> { /* private fields */ }