Changing sizes of media, bleed and crop boxes properly

[Pop, Rares]

Hi,

I need to change the dimensions of media box, bleed box and crop box to some 
arbitrary values.
Typically reducing their sizes to cut the extra space.

I’ve noticed that changing the width and height of these boxes (i.e 
page.setMediaBox(new PDRectangle(890, 990));
causes the content to change its position, like the entire document gets 
re-scaled.

What is the proper way to do this without rescaling the content?

Thank you,
R