How much will a change in input data affect the noise values?

There is no simple answer to this, since a lot of factors influence things. But on page 103 and 104 in the norwegian guide to T-1442 there are some simplified answers.

These answers are based on figures in “Nordic calculation method for road traffic noise” from 1996. E.g. for speed there is a figure 2.3 on page 9 (in the english version).

For effects that give different changes for light and heavy vehicles, this must be taken into consideration. Not that there are some limits, in the nordic method there will e.g. be no change when increasing the speed of heavy vehicles beyond 90Km/h, while for light vehicles the noise continues to increase even beyond 90Km/h.