l have a magnaflow cat back and SPT short ram intake. l beleive its a 20 to 50 shot.

that is all according to how heavy your actuating finger is.

If you shoot it everytime you get the opportunity, your engine will go bad in no time.

no.

Anytime you feed nitrous to an engine not built for it, it is bad news. (ie: stock internals)

If you add a hefty shot of fuel at the same time then you will be ok. Otherwise lean kaboom. The sti engine is tough.

if your tune is good it should be ok. you need the right supporting fuel mods and correct engine control modifications

Even small shots of nitrous like you are thinking about does small amounts of damage to your motor every time you use it. l would get a water/methanol injection system and get tuned for it. It is a safer way to make more power on turbocharged cars.