By default, you can hide VA Hashtags from all solutions only by using the extended context menu of the VA Hashtags tool window that is displayed by holding down the shift key when displaying the context menu.
If you make regular use of this global hiding, you can elevate the related commands to the normal context menu, i.e., not the extended one, by modifying the registry. When you do, global hiding is intermingled with per-solution hiding.
Always display global hiding commands and elevate to the normal context menu by changing the value of DisplayGlobalHashtagMenuItems:
HKCU\Software\Whole Tomato\Visual Assist X\<IDE spec>\DisplayGlobalHashtagMenuItems = 01
Set the value to 00 to restore default behavior.