I tested this out on 3.0.3, and it worked partly. I wasn't able to post a URL with under 10 posts, but was able to private message myself. I had my board shutoff for maintenance, and the TestDummy account was a moderator of a test forum. Maybe that had something to do with it, I'll test it out later.
Just to confirm, this is all that's needed to require registered members to have 10 posts before they can send PM's:
Code:
----------------------------------------
Find:
----------------------------------------
// process errors if there are any
if (!empty($errors))
----------------------------------------
Add BEFORE:
----------------------------------------
$errors = array_merge($errors, verify_message_urls($pm['message']));