You can place multiple EditorAttributes on the property, but the property sheet will only pick the last one that it finds I believe. It only allows multiple for inheritance purposes, so there is no way to tell it which one to choose at design time.
And no, you can't add a checkbox to the category attribute, its simply a name displayed in the property grid at design time.
If you are trying to extend the property grid in the VS editor, then you are pretty stuck, but if you are showing the property grid at runtime, then you can use a different property grid control, like
Telerik[
^]
DevComponents[
^
VisualHint[
^]
Or make/customize your own[
^]
Submit an article or tip