#!/bin/bash

input='/usr/share/libalpm/hooks/90-mkinitcpio-install.hook'
sed '
  /Target = boot\//d
  /Description =/{
    s/=\s*/= Test permissions for /
    a When = PreTransaction\
Exec = /usr/bin/sh -c '"'"'[ -w /boot ]'"'"'\
AbortOnFail
    q
  }
' "${input}"