Inkscape HOWTO

What would be really amazing is if they had constraints like proper CAD software, it would make it possible to not have to redo entire diagrams when you want to change a small part of them.

Bibliography:

It should be noted however that path effects can accomplish some of it.

This is basically a more specialized subset of inkscape constraints:

There's a tiny little crosshair that you can drag around to set the center of rotation.

And there's a button to make that crosshair snap: inkscape.org/forums/questions/can-a-pivotingtransfrom-crosshair-be-moved-and-made-to-snap-to-a-node-or-a-grid-point/#c14432

This is related to the underlying SVG pain point of SVG background color:

For PNG export: