Change of the size of roof windows after building permit

What are you actually planning to do with the windows, do you want to lean out of them and use them as a lookout? - if they are only purely for lighting and ventilation, you can save yourself the pull-ups. For this purpose, windows for use in normal intermediate rafter fields are absolutely sufficient, you must not compare double casement windows with facade windows of the same glass area - presumably this is where the mistaken fear comes from that they might be somewhat undersized (?)

What are you planning to do with the windows anyway, do you want to lean out of them and use them as a lookout? - if they are just for lighting and ventilation, you can skip the chin-ups. Windows are absolutely sufficient for use in normal intermediate rafter fields, you must not compare double sash windows with facade windows of the same glass area - presumably this is where the mistaken fear comes from that they might be somewhat undersized (?)

No, I don't want to lean out and they are actually not a lookout either. I was more thinking about the effect of a "panorama window", which can look very nice, for example in the bathroom, so that the double sash window not only looks functional but also beautiful and harmonizes with the room. Of course you are right and the current size would do as well, but I think wider windows would create a better atmosphere in the room?

Or several (e.g. three) narrow double casement windows next to each other, with only one beam thickness of space between each. The visual effect also looks quite nice in the end and may not be much more expensive than one large window and more effort when aligning the roof truss.

Or several (e.g. three) narrow double casement windows side by side, with only one beam thickness of space between each. The visual effect also looks quite nice in the end and is perhaps not much more expensive than one large window and more effort in aligning the roof truss.

I found in the structural calculation of the house that the rafter spacing is probably 1m. If the carpenters adhere to that, a double casement window one size larger than now would be possible – so 74x118 instead of 65x118. For a width of 94 it would not be enough. But at least. You are right, 2 double casement windows side by side also look very good; I will reconsider this for the hallway or bathroom.

that the rafter spacing is probably 1m. If the carpenters stick to that,

With tolerances, of course, but they do stick to it. After all, the standard sizes for double-wing windows are derived from common rafter spacings. But keep in mind: this is a center-to-center measurement, not a clear (net) dimension.

With tolerances, yes, but they adhere to them. After all, the double casement window standard sizes are derived from common rafter spacings. But keep in mind: that is an axis measurement - not a clear opening dimension.

From which rafter spacing should then 94 cm be derived? The rafter spacing would have to be quite large.
Yes, unfortunately it is not a clear opening dimension, then it would fit.
With a lot of luck, one might even remove a rafter and attach it, gaining a few centimeters. But still very tight for a 94 cm double casement window.