I'd agree with WhoDat....soldering anything onto a circuit board requires a bit of electrical savy; not hard to do, but would require a solder tool (easily bought from Radio Shack), some solder, and a sucking tool to remove the solder when removing the existing led's that are on your current guage cluster.
Acluster that is equipped with the "MyColor" option may be swapable into your Mustang. I know this was an option on the 2011 to 2014 Mustangs, so perhaps Ford offered it on the 2005 to 2010's as well. If it was, then removing your cluster, and replacing with one that has this feature might work. However, on the 2011 to 2014's, the buttons to program the color are on the dash, so this may also be an issue (do you have these?). Another issue is that the mileage from a donor cluster will not match your true mileage, and I do not think most states allow you simply swap a cluster without legally having the mileage flashed to match yours. Then again, most do not care to be complient with such things.
So, maybe just de-soldering and soldering in new leds would be the easiest...
It is better to keep your mouth closed and let people think you are a fool than to open it and remove all doubt.