According to https://docs.vyos.io/en/latest/automation/command-scripting.html there should exist both preconfig and postconfig scripts at following location:
/config/scripts/vyos-preconfig-bootup.script
/config/scripts/vyos-postconfig-bootup.script
However in current 1.4-rolling the preconfig script is missing:
vyos@vyos:~$ ls -la /config/scripts/ total 12 drwxrwsr-x 2 root vyattacfg 4096 Jun 28 05:17 . drwxrwxr-x 9 root vyattacfg 4096 Aug 4 08:28 .. -rwxrwxr-x 1 root vyattacfg 230 Aug 3 12:01 vyos-postconfig-bootup.script