You can turn it off by menu or hotkey; see the Settings file for the available hotkeys. But it sounds to me as if you'd rather want to suspend EPKL? That keeps the program in the background so you can easily get it back up.
In the latest release you can even specify suspendingApps, programs that automatically suspend EPKL while their window is active.
If you want to return to QWERTY but keep Extend and other stuff active, you can have a QWERTY VK layout on switch and just switch to that. Again, there's a hotkey for switching layout, by default Ctrl+Shift+2.