|The Asus Cube (image from Amazon.com)|
I won't go into great detail about getting root on this device here, you can find that yourself. Root is however required to proceed.
Look for this file: /system/usr/keylayout/Vendor_0b05_Product_17ca.kl.
The /system filesystem must be mounted with read/write access. You can do this from adb or the awesome ES File Explorer is able to do this.
Change the following lines:
key 87 KEYCODE_VOICE_SEARCH
key 88 KEYCODE_NETFLIX
# key 87 KEYCODE_VOICE_SEARCH
# key 88 KEYCODE_NETFLIX
key 88 TV_POWER
Reboot the device completely, a good way to do this is by issuing "adb reboot". Another way is to disconnect the power to the device.
Now you can stop accidentally hitting the voice search key and have a "sort of" working TV power key. The reason I say this is because the IR blaster is required, so the newly-added TV_POWER button will not work unless you have the Cube powered up already.
If you don't want to change the Netflix key, you could, for example, change the existing TV/STB key to be TV_POWER. I am not at the moment a Netflix subscriber so this key is useless to me.