I haven’t seen a study comparing cigar and cigarette smoking in MS. I expect there would be less systemic damage from cigars, and the amount would depend on what you mean by occasional.
When I say less damage I don’t mean none, because tobacco smoke can cause cancer in the mouth as well as the lungs. Also, even though you aren’t inhaling smoke directly through the mouth to the windpipe, you are inhaling it through the nose. Otherwise you wouldn’t sense any aroma, and the aroma is most of the pleasure. In effect, you’re breathing your own second-hand smoke. So you’re probably spending some of your quality life time and time to disability on tobacco use and enjoyment.
How much time, I can’t estimate - I’m not a scientist. One thing I’m fairly sure of, though, is that you won’t find an MS neurologist, MS nurse or other MS specialist anywhere who’ll tell you it’s OK to keep smoking cigars.