I haven't even tried it ...
I'm not trying to enable twinview untill I'm shure there's a button or a script out there to disable it for a short time.
Or can I leave it on and just take of the CRT monitor? Maybe this works, I don't know. But I've read that when using twinview on a laptop, the extra CRT monitor becomes the primary device, not exactly what I want when I disconnect it.