Is it safe for someone who had kidney stenosis and undergone stent insertion to have sex?

Definitely. As long as your doctor has cleared you post procedure, by all means enjoy life.
Yes, but carefully. A renal artery stent procedure is almost always a same day procedure. A suture or tiny clip is often used to close the hole in the artery which enables the patient to get up sooner and recover more quickly. Most patients can resume activity in several days and sexual activity within a week or two. Be careful using an ed drug as the procedure will result in lower BP and/or less BP meds. See md.