Certainly not a lot of support on this one! Well let me be the one to actually offer some evidence and support!
First off I say go for it! However you need to find the middle ground because as some have said to make the 12 entirely like a 13 that would be very costly.
Here is what I think you should go for.
Change out the following to the 12 sport:
Grill
Possibly hood but as mentioned expensive
Front and rear bumpers
I say keep with the 2012 bumpers because if you do try to match the front end of a 13 you need a new bumper, fog lights, brackets, grill, not sure about the hood, and a host of other things that we just don't know about yet.
Now change the following out with 13 parts!
Headlights
Tail lights
Badges
Wheels
Door Panels
This will give your Ram a unique look. Honestly this is what I have done to my Ram and I get compliments. I also get many people who think my Ram is a 2013 because they just don't notice the small details that make it a 09.
The cost to do this isn't that bad at all if you are patient. Search ebay hard and you will find a set of wheels easy as well as door panels. Headlights I will recommend JJ. I went through with a retrofit on those. Tail lights I would recommend Mopar Parts Online as they have instructions for a plug and play kit.
Finally enough of my rambling and here are some pictures of my 09, 13 look a like.