I'm almost sure this is the solution, but I'm not sure my method was right. Nevertheless, here it is.
First, let's scramble the main part of the riddle a bit to make some things more coherent:
Now not you try to scratch this
Not means evil one in disguise
With ones flick to change lights
Not write in and for eating
As you can see, it still doesn't make much sense. But if we treat some of the words as commands:
No W, no T: You try to scratch this
No T: Means evil one in disguise
With one S: Flick to change lights
No T, write in 'and': For eating
Now they look like proper clues, all leading to one word:
No W, no T: You try to scratch this (Itch)
No T: Means evil one in disguise (Witch)
With one S: Flick to change lights (Witch+s = Switch)
No T, write in 'and': For eating (Switch-t+and = Sandwich)
[Note that 'itch' is a separate clue, which is why I'm not sure I scrambled this right]
And as for 'I'll never rest':
You're restless when you're twitching.
Again, I'm not entirely sure I got there properly, but I'm fairly convinced that's the gist of it.