Engineering Bootloader G920F - Downgrade 5.1.1 to 5.0.2

as i said in the title,

i know that there is this engineering bootloader that keep safe the knox status if you want to mod the phone.
my question is simple, if i install this particular bootloader, i'll have root and custom recovery, is it possible to install a rom/custom rom/ stock firmware with the 5.0.2?

thanks.