Yes on the switch, if you are replacing the heads for one another. The plugs are all the same on the J1 & J3 plug ins on the back, with the Shakers and 6CD units having an additional J4 plug. The 09 also has a wire harness that runs into the console box, so get that short harness if it available. It makes it so that an Ipod or MP3 can be used from that spot. I'd get everything from the 09 just to be sure. The 09 system is Job 2 (Part number starts with the number 9 and has chrome around the knobs), so you will have a much better set up than with the Job 1 (all black knobs) head you currently have. Job 2's are also Sirius satellite capable, so you can add that or even add a SYNC kit if you feel like it (Job 2 only). You'd need the Sirius box and a pay subscription, but it would all be available with the Job 2 head.
I put an 2008 Taurus navigation system in my 07 Mustang without any problems. There are a lot of interchanges that can and do work, but not all will work correctly. If your radio is set up for a Mustang, F150, Fusion or a Taurus, it will work correctly 80--90% of the time in a Mustang. Some will even work with steering wheel controls, but those had to be in operation originally to work in another car. If they are NOT just turned on from the factory, then the radio head would have to be sent out to have that function set up.
I added a 2013 Boss steering wheel, replaced the switches to fit my radio head (right switches are different with Shakers, regular and Navigation heads). By doing this mod, I have fully usable steering wheel, with functioning audio controls. I added the factory SYNC kit also, and i now have everything working. It is how they should of came from the factory. I don't have the mirror speaker set up, because I added a Homelink mirror, but the SYNC kit came with an add on microphone and speaker, so it works out well. Lol. Hope that sort of helps you out. Good luck with your switch out.
07 Mustang V6, GT 19'' wheels, Bullitt suspension & brakes, Dynomax dual exh w/GT takeoffs, Eleanor style grille, Shelby rear spoiler, CS/GT bumpers, SHR insert, side & rear window louvers, CS/GT scoops, SYNC/Navi, Roush hood scoop, Leather power seats, IUP w/GT MyColor, hood shocks, 8.8 trac-loc w/3:73 gears, logo'd trunk mat, trunk lid storage organizer. Gen 5 tail lights, '12 lighted vanities & outside mirrors, '13 Boss Strg Whl.w/audio controls, Ambient lighting, puddle lamps