This is the script. /home/deck/scripts/fstab contains my customised fstab file. Yes, after an update, I just run this script once.

#!/bin/bash

if [ ! -f ~/.config/kdesurc ];then
  touch ~/.config/kdesurc
  echo "[super-user-command]" > ~/.config/kdesurc
  echo "super-user-command=sudo" >> ~/.config/kdesurc
fi

if [ ! -f /var/mnt/nas ];then
  sudo -c 'sudo mkdir "/var/mnt/nas"'
fi

sudo cp -a /home/deck/scripts/fstab /etc/fstab
sudo steamos-readonly disable
sudo pacman -Syy
sudo pacman-key --init
sudo pacman-key --populate
sudo pacman -S --overwrite "*" nfs-utils
sudo steamos-readonly enable
sudo mount -a