...when Apply and Save button isn't show, it's cause the MCHBAR is locked in Write.
You can check it by: Open WPCRedit on PCIBus :0 Device:0 Function:0 and look at
OffSet F4, bit[0] :if it's at 1, MCHBAR have been locked in write by the bios.
And unfortunately, it's a "read only" bit, You can't write 0 in this bit.