Exchanging existing window for a French door...

One of our bedrooms (old, 1962 house) has a window opening onto a little side patio that is accessible only from outside at present, via stairs.

If we wanted to replace that window with a glass opening door ("French" door), not changing the height, so the bracing above the existing window would stay in place, would this need a building permit? I believe this would not be a structural change.

There is no electrical or plumbing in the wall below the window. In fact, when we moved into the house, that particular wall was the worst in the house. It had major cracks, and you could see daylight through one of them. It has since been repaired. But definitely not structural. In our house, and many that I've seen from the same era, the wall under the window is recessed--I guess for extra space--and is not even the same thickness as the rest of the wall--only about 1/2--maybe 8 cm.

This is not visible from the front of the house, if that makes a difference, and this is not a historical area where the look needs to stay consistent.

Thanks for comments!