Allowed Races function is only used in one area that I can find, and not in the Standard Race specific Techs.
For instance, check Holographic Projections. Allowed Race isnt used, however in-game its Kiadian Only.
It still work. Originally the tech could not be modded you know, when they unlocked it they also added the ALLOWED RACES for every one to be able to do more race specific techs. Before that all you could do was give predefined special techs from race files.
I have already tried it in my own mod, I removed a special tech from race files, and gave it back to that race with ALLOWED RACES. It works, you need to do it for every project though, it does show up in galactopedia as special tech etc...You can give techs to any races you want through this methode.
The only difference I've found is that when you set your game tech level at ''normal'' you dont get the tech free from the start, which is exactly why I like it more, I prefer to force Me and AI to research it.