Shorten roller shutter when converting a door into a window

Hello,

I would like to have a balcony door partially bricked up. A window should then be installed in the upper area.
My question is whether I can keep the [Rollladenkasten] (new box, insulated ...) and only reduce the number of slats.
The [Rollladen] is electrically operated. The balcony door and [Rollladenkasten] are not a unit.
Thank you very much for suggestions
Ecatrin

Well, without at least pictures and drawings of the situation, one can only guess here...