No, it really has nothing to do with the ui_ stuff. The UI stands for User Interface and controls where the aircraft shows up in the list.
What you want to change is a small line under the heading [General] usually located just under the [fltsim.x] entries. Look for atc_type= and change it to whatever you want. Now be sure to note that not just any assignment there will be understood by the program. There is a specific list of types that you can enter here. For more on this, and a list of all the entries you can make, go here:
http://www.homepages.mcb.net/bones/04FS/data/fsdata.htm