If you are interested in the science behind it:
Using the “toothpick method” sends the TV-Box to Android Recovery Mode.
Another method is to execute “reboot /update” from the Android Terminal.
Both work with CoreELEC and neither method should erase data or factory reset a device.
Yes, and as Vascobraga already mentioned in his reply, there are a couple different methods of achieving this.
Again a bit more information here:
One method involves removing or inserting the external medium (CoreELEC card) as needed before powering on the device, another is to always boot into CoreELEC from the external medium, then use the ‘reboot to eMMC’ option from the power menu.
Running CoreELEC from an external medium offers a non-intrusive way of running and testing CoreELEC.
With a compatible unsupported CoreELEC-ng device, one even can have CoreELEC and Android co-exist on eMMC with the ability to dual boot between them.
Caution is suggested when manipulating a device at this level. Creating a backup and having the ability to restore the firmware are pretty much mandatory requirements before attempting these kind of installations.