I have been messing with my rear blade assembly off and on for the past couple weekends in 5-10 min stints, usually before leaving to go somewhere. Seems like I have to almost break something to get it to come loose, dunno if it's just stuck from road grit or what. Logically, the blade should be replaceable, so I'll take it off the truck and get a closer look at it soon.
I can definitely see why your dealership would sell the entire assembly and not the inserts as it seems to be a point of confusion for even the dealerships. My dealership gave me a Scion 12'' wiper blade when I asked for a replacement blade. It's a silver color and looks different on the ends so I'm not sure if it will fit even if I chop it down on either side. Gonna have to go back there I guess and see if I can clear this up.
It's rather ironic really that this is even an issue for people at all, but nonetheless, here we are.