All psionics skills in my Star*Drive campaign are untrained skills.
While any character may potentially have psionics powers, I limit them to characters who dedicate themselves to the use of such powers (generally as Mindwalkers, spending a lot of points in psionics skills), not as a small perk or side effect.
Designing Special Weapons
Characters may design special weapons. But to avoid that my campaign be spoiled by too deadly weapons, I only entitle the players to slightly amend the characteristics of the weapons detailed in the Player Book.
As a rule of thumb, I allow the players to modify a standard weapon to do one level higher damage (D4 becomes D6, D6 becomes D8,...), but that weapons suffers instead a one step malus on Accuracy and the Range is halved.