Document update based on ID

[Evgeniy Strokin]

Hello,.. 
I have a document indexed with Solr. Originally it had only few fields. I want 
to add some more fields to the index later, based on ID but I don't want to 
submit original fields again. I use Solr 1.2, but I think there is no such 
functionality yet. But I saw a feature here 
https://issues.apache.org/jira/browse/SOLR-139 and it looks like what I need.
Is it implemented already? How can I get the code? Would you suggest to use it 
in production? How it works? 
 
Thank you
Gene