Add new encoded value for air_quality

I, i want to extend the functionality of graphhopper.
I want to create a custom profile that calculate a route between point A to point B in a city of Bologna based on pollution.
For achieving that, i want to add a new encoded value to all edges with a random value from 0 to 1.
After that i want the routing algorithm to take into consideration also that encoded value to calculate the best path.
For now I uploaded my pbf file of Bologna but i have difficulty to add new encoded values and adding a random value to all edges.
Can you please help me in achieving it?