This article shows how to disable a Wacom tablet without unplugging it physically. This could also be applied to other input devices, but in my experience I only use it on Wacom tablets.
Why am I interested in disabling the device? Well, some programs have problems dealing with multiple devices, and the "tablet inside" a Tablet PC cannot be easily unplugged, making it harder to use a external tablet.
Disable the device
Open a terminal window and run:
xinput set-prop DEVICE_NAME 'Device Enabled' 0
DEVICE_NAME can be determined using the command
xsetwacom list devices. If
DEVICE_NAME has spaces you should surround it with quotation marks (either single or double), like so:
xinput set-prop 'Wacom ISDv4 E6 Finger touch' 'Device Enabled' 0
The device could be easily enabled again replace zero (0) at the end of the command with a one (1).