Yuku free message boards

The rule regarding changing logos was actually instituted because of the National Association's contract with New Era some years ago. New Era agreed to keep an inventory of affiliated minor league hats (to make for rapid order filling) and to push the retail sale of hats. However, New Era was concerned that minor league teams might change logos rapidly, which would make the inventory obsolete--and waste their money. As a concession, the NA agreed that teams would would have to keep a name and logo for at least three years. After three years, a team was free to change names or logos, but then a new three year clock would start ticking. The exception to this rule was if a team's name was based on its Major League affiliate, in which case a club could change its name within the three-year window if its affiliation changed.

Having been out of affiliated ball for a few years, though, I can't say whether the rule has changed recently. But the reason for the rule was the deal with New Era.