anarcat/base.pp

## base.pp
class base {}

## common.yaml
classes:
 - base::includes

## example.com.yaml
classes:
  - role::rt

## includes.pp
class base::includes {
  include profile::postfix
}

## postfix.pp
class profile::postfix($override = false) {
   class postfix { override => $override }
}

## rt.pp
class role::rt {
  class { 'profile::postfix': override => true }
}

## site.pp
include base
hiera_include('classes')
	class profile::postfix($override = false) {
	class postfix { override => $override }
	}
	class role::rt {
	class { 'profile::postfix': override => true }
	}