What sort of changes are you going for?
Certain aspects, I am lead to believe are hardcoded and can't be amended, eg Cloak/Decloak rate - although if anyone knows differently on this one in particular, I'd be delighted to be corrected!!
Other items are very easily amended, such as weapons damage, shield and engine strength, speed and maneouvrability, and the item's resistance to damage. If you highlight the effect you're afer, I can hopefully point you in the right direction.
There could very well be limts to how strong you can actually make an item, but I am unware of these limitations. Simply changing the Damage level should be enough to increase a weapon's strength. Try setting one weapon to a ridiculously powerful level - make Damage say around 500 and watch the impact of that weapon on your test opponent... However, being able to destroy something in a single shot is a shortlived novelty and makes for brief but boring gaming.
MajorRacall