Composer install on existing project with customization overwrites them

[johnbburg]

Perhaps I am doing this wrong, but I have an installation of pattern-lab, and we've added some new functions in source/_twig-components/functions/. However, when installing from scratch, (this can be recreated just by deleting the /vendor directory), pattern-labs postInstallCmd script will remove these customizations. For example:

the path ./source/_twig-components/functions already exists. merge or replace with the contents of pattern-lab/drupal-twig-components package? M/r > 
contents of ./source/_twig-components/functions have been replaced by the package's content...

It seems the the default (M)erge option shouldn't do this. Any suggestions?