Hi.
If you are using an unatended file you can delete the domain name used to join the domain and then it will ask you to enter the domain name in the same section as the part where you define the computer name, so you can enter it each time.
<network_identification skip="0">
<computer_name />
<!-- 0 = Domain, 1 = Workgroup -->
<membership>0</membership>
<domain>REMOVE WHAT IS HERE</domain>
<domain_options>
<option></option>
</domain_options>