Is there a chance that you could add a new airline
Airline : SKYWORK
CallSign : SKYFOX
If you can do the voice file editing (e.g. "sky" from "Aerosky" and "fox" from "Aero Fox"), it is easy to add it youself:
Inside the PF3 directory you find the files:
captions.ini with lines like: Pfac167=Aero Fox
Data/pf3_callsigns.dat with lines like: Aero Flight,167,10
Wav/StdX/pfac167Y.wav (with region X and voice inside this region Y) contains the spoken callsign.
Wav/RadX/pfac167Y.wav (same as above, but with radio distortions)
Just find a pfac entry in captions.ini that you no longer need (I don't know, maybe you can even use an unused number?) and change this to your airline, e.g.:
PFac1000=Skyfox (this replaces Ukraine West)
Now add an entry in Data/pf3_callsigns.dat (it can contain duplicates): Skywork,1000,10
(the 10 is for region Germany, look at the other airlines if you want a different region)
Now overwrite the pfac1000?.wav files (yes, they are 238 such files!) with your edited versions.
Alternatively edit fewer voice sets and exclude those you did not edit in PF3's options #2, but if you edit all of them and send them to Dave, I can imagine he includes them in the next update.
Edit: For first tests you might want to use "pfac900=Skyway Ex", they already sound similar enough to Skyfox, and changing the text is easy