Download and install ACS Commons.
How do I package ACLs from one AEM instance and install them to another?
To migrate permissions between AEM environments, you can use the ACS Commons ACL Packager:
Go to http://aem-host:port/crx/packmgr/index.jsp and log in as admin.
Click ACL package.
Select the Advanced tab (see screenshot below).
In the AC Handling dropdown menu, select Merge to avoid removing existing ACLs on the destination system. This is especially important when migrating ACLs between different versions of AEM (as it avoids removing out of the box ACLs).