Have been using nuvaring for years, is it ok to replace it & skip the week off for 3 months and then take the week off?

Skip one week first: I would start skipping one month first to see how that impacts the menstrual period following the skipped one. If that menstrual period is not heavier and longer than what the periods are now, i.e., if there is no indication of the hormones showing a cumulative effect, I would then skip two periods and so on.

Yes you can...: Nuvaring instructions are to leave it in for 3 weeks and then take it out for a week. Research has shown that it is also safe to leave the ring out for only 3-4 days per month. You can also leave it inside for 28-31 days and then change it without a break. You will still be protected from pregnancy and it's safe for you. Some women will have irregular spotting doing this. Best wishes!