Custom Role: Remove the Merge Button on Cases records

The Merge button available on Case record is dependent on Duplicate Case Management permission assigned to the role. Administrator can perform the following steps if access to the Merge button should be limited:

Here are the steps:

1. Navigate to Setup > Users/Roles > Manage Roles.
2. Edit or customize the Role in question.
3. Click on the Permissions tab > List subtab.
4. Remove the Duplicate Case Management permission.
5. Click Save. 

This removes the Merge button on case records for users logged in with that custom role.