As Sage Ambassador told that I am not able to change settings in any way, I am rising an idea to solve my problem.
For NI users who are selling to EU and using T4, now under the Default Tax Code with T4 code in it the box "Use Default Tax Code" tick box is grey, not active, what means that when I posting a sales order, regardless of the default settings of the customer, the product lines come up with Vat T1 and I need to amend them manually, each line and for each customer.
When in our business there are 95% of EU customers, this limitation becomes a big issue.