Bitbucket 4.x completely changed the branch permission model that previously existed with Stash. While Bitbucket still refers to the concept as Branch Permissions, the documentation actually indicates that the new model is really a branch restriction model - "... are actually restrictions, which are checked after project and repository level permissions". And, in fact, the model is restrictions with exceptions by groups or users. Keyed by restriction and matching type, different restrictions can be added.
We have decided that the CLI needs to reflect the terminology of the new model and discard the older terminology in order to avoid confusion in the future. While it is understandable that Atlassian has chosen to keep the older terminology at least for now to reduce the impact of the change on documentation and because the UI can mask the confusing points, we feel the same is not true for CLI action names and terminology.
The result is we have made some significant incompatible changes related to Branch Permission related actions. As a policy, we rarely make incompatible changes like this, but, in this case we feel it was warranted.
Discontinued Stash Support
With CLI 5.6, we are no longer supporting Stash 3.x. We didn't want to confuse the branch permission issue further by trying to support both models at the same time.