The answer
Yes. You can enter the custom nameservers assigned to your domain in your account. You then maintain DNS records in their corresponding DNS management service. Registration and domain management stay with atdomain.at.
Records in the atdomain.at DNS tab control resolution only when our default nameservers are used. Copy existing values before switching and test every service afterwards.
What to do
Prepare the new DNS zone and all required records.
Save the assigned nameservers in your account.
Make future DNS changes in the active zone.