How flexible is a building permit?

Regarding my extension and the thread about symmetries, I have a question about building permits in general. How flexible is such a permit? That is, what can be changed without involving the authorities, risking a fine, or not getting the construction approved (final report). For example, the width and height of the windows? Built 10cm wider than planned? So rather small things that do not completely turn everything upside down. If larger changes should occur, does the permit have to be renewed? Or is the office only informed. Not to be misunderstood, nothing is planned by me. Just for gaining information and for the case of emergencies.

You can do quite a bit with a supplementary amendment. It costs about a hundred (or so) and doesn’t take as long as the approval itself. Building height, distances, exterior colors, etc. should be done through that, so everything that concerns the requirements of the development plan / state building regulations and might deviate from them. Moving a window, 20 cm bigger or smaller, anything that concerns the floor plan and arrangements, the building authority isn’t interested in.