It's not possible to cancel to process once you selected once you selected 'Paste Entry'. It produces an error.
- Open the LDAP Browser view
- Select an entry (Copy Entry / DN)
- Try to paste it to the parent of the selected entry
You get the "Select copy strategy" box, which contains only an "OK" button. Even when I try to close the box I get an error box, saying that the entry already exists (LDAP: error code 68)