What is the best way to add user points to existing users I have a dev and prod versions of my D7 site. On dev I developed some functionality based on User Points module and plan to roll out it on prod. But it requires some initial number of user points for every user.

What is the best way to add user points to existing users: SQL query, Rules etc?
One method here is to use the Userpoints API and execute a code snippet that will add the points for you. You can reference the userpoints API here. You can do something like this...

$initial_value = 10;
//@TODO: Build a list of all $uids in an array
foreach($uids as $uid) { =
  userpoints_userpointsapi(array(
    'uid' =&gt; $uid,
    'points' =&gt; $initial_value,
    'operation' =&gt; "Add Initial User Point Value",
  ));
}