You can't turn off blocks of memory in a single RAM chip AFAIK, it's all or nothing. And I think enabling and disabling different RAM chips wouldn't be very via

You can't turn off blocks of memory in a single RAM chip AFAIK, it's all or nothing. And I think enabling and disabling different RAM chips wouldn't be very viable since you'll need to move memory from one chip to another when turning one off, there would be a lot of potential issues when that happens. However enabling and disabling RAM chips and rebooting the laptop, like a low-power toggle, would be possible.