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).
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