J.W.
Pulling credit dings your credit as does changes to your debt ratio. It should rebound when your new mortgage hits the credit bureau. Before that they only know you are getting a mortgage but have no idea how much.
Granted if it is higher or the same as the assumption it may stay the same but if it is lower than they assumed it will go back up.
Pulling credit hurts because all they know is you applied with X but they don't know what is the product or the amount.
Breathe