Thank you NiLuJe, I will take a look.
My last idea was to extract rootfs.img from the 5.10.0.1 factory .bin package and use it to flash the system partition (fastboot flash system rootfs.img) -- if 'flash' command is not locked
NiLuJe and knc1, as kindle hack dev gurus, does this idea makes sense to you or do you think this is a stupid idea ?
Anyway, I will not try this until the XMas and New Year celebrations are over (I need too much of my kindle during it
)