The answer to your question depends on how much inflammation you currently have which can be determined with a flexible endoscope in your GIs office. I tried to wean off the Rowasa enemas once and, for me, it just wasn't possible because I still had a lot of inflammation in my rectum and sigmoid colon. When I reduced the Rowasas, my symptoms got worse and certainly that is the thing you need to watch out for if you are to proceed with reducing them. If you suddenly start going more, seeing blood, mucus, or have increased urgency then certainly go back to nightly again.
Are you taking any other meds besides the Rowasa? How about
oral meslamines? As you are never going to be off meds entirely with uc, just a fact of life. We're all pill-poppers here out of necessity