Take a look at this thread https://groups.google.com/forum/#!searchin/tasker/silent/tasker/4ClJf95kRpE/yeJkSyhOzSMJ
There is an action Interrupt Mode, it was added in 4.6. I believe Pent said the best practice would be to use the %SILENT variable to check for silent, but use Interrupt Mode to set the mode for Lollipop+.