Question of doing Pyeloplasty on a 2-month-old child is not so much of safety, but need. There is no other treatment or choice that you have. It must be done and it is reasonably safe in competent hands. The risks involved are of any standard operation. If done in a centre that routinely handles babies of this age, there are no major worries.
No, this fault cannot be rectified without surgery. Surgery corrects the fault in 98% of cases.
The right kidney will be normal. The left will never be completely normal. The aim of the operation is to protect against further damage to the left kidney. There are no side effects and the child can have a normal lifestyle. The child can most certainly participate in outdoor games and activities that require physical strain. There is no need to take any future precautions.
There is no doubt in my mind that the best technique today is still the standard open operation and not laparoscopy.