If you registered domain.ie and you would rather have domain.com or mydomain1.ie, then you must register the domain as new name.

This means you will own both names. Once the original name is due to expire, simply choose to not renew the registration. Domain names cannot be changed once they have been registered.
However, if you have ordered an IE domain name and the application has not yet been approved by the IEDR, we can change this domain name for you at no extra cost.