Can I do that with my 07, how do I do it, and will it increase mileage at all due the better atomization?

 

Yes you can cap your sensor on your 07, I will take some pictures of the motor in the garage when I get home and post them with step by step instructions on capping a rail on a CR 5.9.

 

What does capping the rail accomplish?

 

By capping the rail you increase rail pressure. If you have a weak rail pressure blow off valve it will release pressure too soon and cause your rail to "drain". One of my friends actually had his rail pressure cap blow causing the rail to drain all the time. Instead of buying a new valve we capped it internally and he has yet to have a problem with it and has run up to 25k PSI iirc.