Answer:
No, unfortunately this is not possible.
If the "Tension Stiffening" option is not applied for the calculation, the damage parameter ζ is either "0" for "uncracked sections" or "1" for "cracked sections". For this, see the technical article about the distribution of the damage parameter ζ under Downloads below.
Nevertheless, the manual specification of ζ = 0.5, for example, is not possible.
