Yes, you can retard the timing on it yourself but probably not enough. So you should get a nitrous file for it and in addition the fueling may not be best for nitrous if it was set up NA.
TBH I'm not sure if my 03 has one but i have a friend with a 98 and he told me his cuts around 135. Only time ive been in that range is under spray and for fear of going lean ive always cut off about 125. Well going lean and the stock suspension and brakes scare me at that speed.