Is there a way to changed the display style from "WEAVE" to "25% HATCH" for all blends at the same time or must this be done for each blend in a pattern?
And can you set a default so all blended floss added will have the display style you prefer?
It looks like the answer to both of your questions is "no".
The options for display of the blend is only available on a case by case basis so there is no way to define multiples at one time. There are generally few blends compared to total colors in a patterns so that may be why there is no global option. There is also no "option" to define that as a default.