How can I add my own steps to build a paclet

[kirillbelovtest (Kirill Belov)]

Hi all, I use the standard paclet-notebook to develop, build and publish my packages to the Wolfram Language Pacet Repository. But the build process itself, which results in a .paclet file, is always standard. I have some external libraries that I build manually using a special script called Scripts/Build.wls in the project folder (it doesn’t matter what they are now). How can I add a call to this script at the moment when I click on the “Build” > “All” button?