I want to make a calculated field to be not readonly.

I did not find a way, because it is hardcoded, that a calculated field
is allways readonly.

Problem:
Table has two fields:
amount (without vat)
vat

The form has 3 input fields:
amount (without vat)
vat (readonly)
amount (with vat) (should be editable)

The "Amount with vat" Field is a calculated Field and should be
editable. If the user change this value, the OnValidateField Event
then would change the values for "amount without vat" and "vat".

Any suggestions to solve this problem?

Thanks,
Andreas