Restrict Change Assignment Action List for Managers

Summary

We need to restrict the list of Change Assignment Actions available to Manager

Content

We would like to make the Change Assignment functionality available to Managers but only want them to have access to one action.  I have seen a few posts that suggest that this functionality will be available potentially in 20B but is anybody aware of a workaround? 

Is it possible to use Page Composer to default an action into the 'What is the action name?' then we could hide this field so that this is all they can do.  We would create a rule against this action to only display the fields they can update.