I didnt check your file, but the solution is sth like this
fc = "your_featureclass"
fields = ["road_name_field"]
cursor = arcpy.da.UpdateCursor(fc, fields)
for row in cursor:
full_name = []
full_name = row[0].split(" ")
road_type = full_name[-1]
if road_type = "ST":
full_name[-1] = "STREET"
elif road_type = "RD":
full_name[-1] = "ROAD"
result= full_name[:-1]
result.append(full_name[-1])
row[0]= " ".join(result)
cursor.updateRow(row)