I believe Nouveau driver can be easily unloaded using modprobe:
modprobe -r nouveau
Also there is an option -b which blacklists it.
-b, --use-blacklist Apply blacklist to resolved alias.
In the web address you attached there is :
option nomodeset
I guess it is a kernel option not to load !ANY display drivers.You wont always need to update initramfs, only if module is included in initramfs you need to update it.
You can check it using one of initramfs-tools by :
lsinitramfs /boot/initrd.img-4.9.0-5-amd64 |less
However if you need to update or rebuild initramfs there is a way shown in CentOs Wiki :
https://wiki.centos.org/TipsAndTricks/CreateNewInitrd