only users beloning to group 'Manually' should be able to merge partners from the partner list views (action 'Merge automatically') Use <record id="crm.action_partner_merge"... to change only affected field.

partner_deduplicate_acl/wizards/partner_merge_view.xml

@@ -8,24 +8,20 @@
         <record id="base_partner_merge_automatic_wizard_form" model="ir.ui.view">
             <field name="name">Restrict automatic merge access</field>
             <field name="model">base.partner.merge.automatic.wizard</field>
-    <field
-        name="inherit_id"
-        ref="crm.base_partner_merge_automatic_wizard_form"/>
+            <field name="inherit_id" ref="crm.base_partner_merge_automatic_wizard_form"/>
             <field name="arch" type="xml">
-        <xpath expr="//button[@name='automatic_process_cb']"
-               position="attributes">
-            <attribute name="groups">
-                crm_deduplicate_acl.group_automatically
-            </attribute>
+                <xpath expr="//button[@name='automatic_process_cb']" position="attributes">
+                    <attribute name="groups">crm_deduplicate_acl.group_automatically</attribute>
                 </xpath>
-        <xpath expr="//button[@name='update_all_process_cb']"
-               position="attributes">
-            <attribute name="groups">
-                crm_deduplicate_acl.group_automatically
-            </attribute>
+                <xpath expr="//button[@name='update_all_process_cb']" position="attributes">
+                    <attribute name="groups">crm_deduplicate_acl.group_automatically</attribute>
                 </xpath>
             </field>
         </record>
 
+        <record id="crm.action_partner_merge" model="ir.actions.act_window">
+            <field name="groups_id">group_manually</field>
+        </record>
+
     </data>
 </openerp>