I know that I can keep aspect ratio when scaling images by pressing the Ctrl key.
But I really don't like this default.
Is there a way to modify inkscape, to make scale and keeping aspect ratio the default?
When scaling an object with the mouse by dragging the corner handles it is quite handy to lock the aspect ration to preserve it. This is done with a small lock symbol in the top panel:
Currently Inkscape doesn't support settings like this to be embedded in default templates.
A couple work arounds are to just hold down the Ctrl key while dragging the corners.
Or, once you create an object and lock proportions any new object you create will automatically have its proportions already locked.