Manual wrote:Blur
Set to 1 to enable Aero Blur on Windows Vista or later operating systems. If no BlurRegions are specified, the entire skin background is blurred.
It is because the [Rainmeter] section, and thus any changes to the blur region, is not dynamic, and thus won't see any change made by !SetVariable or !SetOption or any other dynamic change to variables or options used in that section.
In this case, the skin initially has a width of 200, and that is all any options in [Rainmeter] will ever see.
I'm not an expert on using the blur functionality, but I think there are other approaches that you can use by removing and recreating a blur region with bangs specific to the functionality:
Although our current docs are not clear about this, I should make note that the entire "blur" functionality does NOT work under Windows 8. Microsoft removed the entire concept from Windows 8. I will update the docs so there is no confusion.