When the care package drops you can see what is in it like normal. If you don't want what's in it you can tap X twice to reroll it.
From the wiki:
Hardline reduces all killstreak requirements by one. Its pro version allows the player to "re-roll" any killstreak crate by double-tapping the action button, which will change its contents randomly. A crate can only be re-rolled once, and will always change its content.
While not yet released, a patch announced on December 4, 2010 will restrict Hardline Pro's re-roll to Care Packages only. The SAM Turret, Sentry Gun, and Valkyrie Rocket crates will no longer be re-rollable, greatly limiting its usefulness.
The chances of getting something good are slightly better though. Source