replacing public ip with private in /etc/hosts

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I am trying to replace public ip  with private ip in /etc/hosts for bulk of hosts . 

Current setup

PUBLIC_IP   hostname  shot_hostname 

Needed :

 

PRIVATE _IP hostname  short_hostname

How I can do it using ansible? I wonder if it can be done using gathered facts by ansible? 

I would think of , getting the public ip and register as  variable and same time get the private ip . 

Now, replacing it using replace or inline module. Any best approach ?