Here's how I'm implementing difficulty:
I have all the offsets for shield/armor etc programmed, along with stock base values. So for example, the Hornet has 40 value = 4.0 cm front shields. If you enter a multiplier of 1.5 for difficulty, it becomes 40 * 1.5 = 60 (or 6.0 cm in game).
All TCN ships (that I know of) will have their values adjusted accordingly, so that basically everything becomes either harder or easier.