Sharing rules should be used when a user or group of users needs access to records not granted them by either role hierarchy or organization wide defaults You cannot change the specified groups or roles for sharing rules.
When you transfer records from one user to another, the sharing rules are reevaluated to add or remove access to the transferred records as necessary.
Sharing rules apply to all new and existing records owned by the specified role or group members
You can edit the access levels for any sharing rule. You cannot change the specified groups or roles for the rule.