How to migrate ACLs from one AEM instance to another

 Download and install ACS Commons.

To create an ACL package, follow the steps on ACL Packager.

Go to http://aem-host:port/crx/packmgr/index.jsp and log in as admin.

Click ACL package.

Click Edit.

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).