I want to customize /application/Espo/Resources/metadata/clientDefs/Email.json using the/custom folder.

What do I have to put in /custom/Espo/Resources/metadata/clientDefs/Email.json ?

How would I use __APPEND__ in order to preserve "Reply to All" and "Forward" actions,but override the "acl" part of the "Reply" action?
Do I just put the whole section in the file like this? I would like to make this modification update-proof.

{ "menu": { "detail": { "dropdown": [ { "label": "Reply", "action": "reply", "acl": "create" }] } } }

And how do I change ACL of the "Create Call" button in list view ?

if i add this to the call.json it just shows another button, but I want to change the actual create button for calls.
"menu": { "list": { "buttons": [ { "label": "create", "action": "create", "style": "info", "acl": "delete" } ] } }