I am assuming you are talking about taking an IQR from 121 to 144...and if so the answer is very much so a yes on the tunnel extension...lots of places make the extensions so it won't be hard to do!
Tracks USA makes nice tunnel extensions. About $100. I just put a 121 to 144 on my 2002 Edge. Looks factory, just doesn't look like an RMK due to the way the coolant flows on the RMK's.
check out van amburg as well. They are priced a little more, but quality is much better/stronger than tracks usa from what i've heard. I'm waiting for my bumper extension to come in from them as we speak.
what cooler? the coolers in the tunnel just stay where they r. u need to drill out a few rivets, drill holes for the crossover tube and rivet it back up. unless u have the rr cooler installed. but even then nothing should really change.
get the vanamburg it way nicer then the tracks. i was extremly disappointed with my tracks usa extenstion it didnt last but half a year and bent all to hell.