Effect of liquified hazelnuts on chocolate tempering? I would like to ask if roasted and liquified hazelnuts will negatively affect the tempering of milk chocolate? 

I have hazelnuts that I have roasted and liquifed by using a high-quality blender. Subsequently, the hazelnuts were passed through a strainer to filter out large nuts.

During the high-temperature phase of chocolate tempering, I plan to add the liquified hazelnuts and the 1/4 unmelted chocolate (seeding method). Will my temper be negatively affected?
You are making Gianduja - and if you make chocolates out of it, they're Giandujotti - singular form Giandujotto; The name might help you find sources of information.

The tempering process will be basically the same (I've seen sources suggest 2°C below temperatures for white chocolate temperatures at all times), but keep in mind that it won't be as melt resistant and as such not particularly good for enrobing.