In premiere when you convert a footage into slowmotion (60% blayback for example)
frame blend will be automaticly be applied!
My question is: does aspect HD also output the frame blend in the final result?
Because it doesnt seem to work in the preview window? I see a red cross in my preview window over my image!

That is why there is a red bar, we can't play the frame blending in real-time. Render it or export it and the frame blending will be present, unless you choose to turn it off.

can you turn it off and then on final export turn it on.

in other words, edit with frame blend off (it could be hundereds of clips) and the flick a swith before export and frame blend will be on (albeit with render needed)>

didn't think so