Here I go again... I think I am a bit audacious...

(but now with the rescue pack onboard, just in case...)
Well, once restored my kindle, I have tried again to modify the margins. No way! This time I have modified the three last values (50-100-150 to 10-20-30), which are the ones that worked (until I turn the page...) and also the other values (50.94-33.96-16.98 to 12.74-8.49-6.38) (
ref post #103). The result is the same: I get the right margins, but they are reverted to the default as soon as I change the page.
Any idea?