Changing boot options through kickstart

[CLOSE Dave]

Documentation tells me that kickstart allows an --append switch to the 
bootloader command to add additional text to the GRUB2 boot line. I 
haven't experimented with this and it is unclear to me if the change 
goes only into /boot/grub2/grub.cfg or if it is also put into 
/etc/default/grub. But adding things is not my objective.

I want to delete "rhgb" and "quiet" on the boot line, preferably in both 
places. Is there any way to do that through kickstart or do I have to 
use a post-install step?