You can already change packages in Hiera by using
<pre>
ssh::packages:
  - 'SUNWsshdr',
  - 'SUNWsshcu',
  - 'SUNWsshdu',
  - 'SUNWsshr',
  - 'SUNWsshu'
</pre>

You can access any parameter in Hiera in the format <pre>class::param: value</pre>