Regional, lower-tier, and other national leagues do often serve as test beds for rule changes in major sports.
NBA frequently uses the D-League...excuse me the G[atoraide] League to test out possible rule changes. They also do similar test during their annual Summer League for rookies and young players. FIBA basketball uses different rules and the NBA studies how they impact games. NCAA basketball plays exhibitions under different rules - and sometimes real games- before applying them across the organization. Last season a number of games were played with a new 3-point line (further back) and this season it's applied everywhere.
The short-lived AAF had a number of differences in rules from the NFL, largely in pursuit of finding "a better television product." Their semi-official partnership with the NFL seems to have been the origin of some of the ideas, and the NFL monitored their impact on the games played in the aborted first season. Likewise, NFL Europe had some unique rules that the NFL used for testing their impact.
MLB will test changes to rules and equipment in AA-level ball and sometimes in independent minor league ball, a recent example being the weird padded pitcher's hat was introduced into minors first. Baseball rules are different in other markets, especially in Asia, and some of these have been factored into baseball's international governing body for "International rules" baseball.
NHL? Same verse. Minor leagues, preseason, international rules play, etc are all used to test out possible changes to rules and equipment.
Simply put, it's actually super common in major sports for rules to be different in different organizations, different territories, or different levels.