a quick rundown how to edit boot.scr to change the used kernel cmdline:
mount SD to /mnt on your PC;
cp /mnt/boot.scr ~/boot.script;
.... drop the binary header from the half of the first line (the line should start with the word fatload afterwards);
make your edits;
sudo mkimage -A arm -O linux -T script -n 'Ubuntu Boot Script' -d boot.script /mnt/boot.scr;
unmount /mnt
a quick rundown how to edit boot.scr to change the used kernel cmdline:
mount SD to /mnt on your PC;
cp /mnt/boot.scr ~/boot.script;
.... drop the binary header from the half of the first line (the line should start with the word fatload afterwards);
make your edits;
sudo mkimage -A arm -O linux -T script -n 'Ubuntu Boot Script' -d boot.script /mnt/boot.scr;
unmount /mnt