Hi!
When it comes to baseball scholarships, I think its fair to consider new opportunties as they become available, simply because all possible offers aren't on the table at the same time. There are so many variables in baseball... different signing periods, spring season performance, the draft, etc. Some players may not have their best options available for consideration in the fall, which makes it very difficult to make an informed decision...especially for a 17 or 18 year old.
Evaluate each opportunity at the time its presented, research the committment rules, and be honest with the coach about your intentions before signing. If new opportunities present themselves down the road, reevaluate the situation, follow the rules, and be honest with the coaches involved. More often than not, they will understand.