Rootsmagic lets you add the facts you want to a person. If a couple was not married, then you don't add a marriage fact. Since there is no marriage fact, it isn't possible to enter not married in the place field. It kind of voids the purpose of being able to leave out that fact, if you add it simply to put not married in the place field. Rootsmagic also lets you create events or facts, and I have one called not married (See my reply to ludlowbaylive for the link to an example of a created event).