You cannot specify name of download file through selenium. However, you can download the file, find the latest file in the downloaded folder, and rename as you want.
Note: borrowed methods from google searches may have errors. but you get the idea.
import os
import shutil
filename = max([Initial_path + "\" + f for f in os.listdir(Initial_path)],key=os.path.getctime)
shutil.move(filename,os.path.join(Initial_path,r"newfilename.ext"))
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…