This is true but would would have ALL Verizon cellphones in range connecting to the Stingray. Obviously a warrant wouldn't allow that. The PRL modification would set the target's phone to look for the Stingray (on a separate network) first and a Verizon network second. That would prevent any other Verizon user in the area of the Stingray from connecting to it. What you talk about is possible though and is done by hackers every now and again
The biggest problem with a MITM attack on cellphones is when the target phone is connected to the rogue cell site, they cannot get any incoming calls. Outgoing calls can be routed through an alternate path but, unless Verizon gives you a connection to their switch, incoming voice, email, text will not be intercepted.EDIT:Rogue not Rouge! Sometimes even with spell check these things happen.