"not as usual" is correct and can be used in written English.
It is used to indicate that something is not happening in the usual way. For example: I woke up late today, not as usual.
The conveyance in our rainwater harvesting system is not as usual as the roof drain conduit, which is usually composed of a series of gutters, downspouts and pipes that conveys precipitation from the roof through the piping and to the cistern.
Eich, E. Business not as usual.
It comes from the article "In Sun's Glow, It's Still Business, but Not as Usual".
The figures are faceless (when they are not, as usual, seen from the rear).
The biggest issue on the doorstep this time is not, as usual, transport, but instead the appalling housing shortage.
In every bar you hear evidence of a keen musical mind applied not – as usual – to the single poem or sequence, but the unfolding subjectivity of a journal.
All a person has to do is know his mind about things, which isn't as usual as it seems.
2.42pm BST "Stoked that Aus didn't as usual capitalise from 2 pens gifted by England" says Andrew Williams.
This is not normal, this is not politics as usual.
If they demonstrate that this is not business as usual, we will not revert back".
Maine said his fastball was not as good as usual.
