Written in stone?

[Suicide Junkie]

You can add components to the end of the file without ruining your savegames.

You can't alter the racialtraits file without invalidating savegames.

I'm not sure about the techarea file, but I suspect you could add to it without too much problem.

If you want only a specific subset of the players to be able to use the new tech, you should get all the players to choose a different, newly added "dummy" racial tech before the game starts.
Something like "Player 1 tech", "player 2 tech" etc.
Then the GM just sets player 1 as a requirement for the component. For multiple players, make identical components, one only allowed to P1, the other P2.

Remember that this not only applies to components, but to ship hulls, facilities and units too.

Many abilities can be added to ship hulls, not the least of which is Master Computer.
Since this MC is part of the hull, it cannot be destroyed, so your ships are immune to Psychic A.S.ers