Currently there is no way to edit the super rates. Below is a clip from the help file explaining what is being calculated:
When placing and modifying a road, superelevation is automatically calculated using AASTHO method 5, based on the road design speed.
When the design speed is <= 80km/h, the software uses the 6% table. The 8% table is used when the design speed is greater than 80km/h.
When the design speed is <= 45mph, the software uses the 6% table. The 8% table is used when the design speed is greater than 45mph.