As the next big cdist release is approaching, here is the first gem 2.2 will contain: The type __update_alternatives allows you to configure alternatives on Debian systems, just like any other parameter of your system:
require="__package/vim" __update_alternatives editor --path /usr/bin/vim.basic
See https://github.com/telmich/cdist/commit/84f2ca0d1f59f3f2157d4350de65800a0a759459 for the introduction of the type