E.g. I have a picture with print size 10x20 cm and resolution 300 PPI. How can I change PPI to 200 and keep the print size 10x20 cm? Size in pixels should also change of course. GIMP always does vice versa. It preserves the size in pixels and changes the printing size. Very annoying behavior by default and no obvious way to change it. It drives me mad.
In GIMP GUI terms in "Scale Image" window I want to be able to change "X resolution" and "Y resolution" (pixels/in) and have "Width" and "Height" (px) changed respectively. Or in "Print Size" window change "X resolution" and "Y resolution" (pixels/in) without changing "Width" and "Height" (mm). In fact none of the windows does the thing. What's the purpose of having two different windows "Print Size" and "Scale Image" if they do pretty much the same?!