How to change NAST-VSZTP using program?

Hi,

I got a requirement that to change the NAST-VSZTP based on certain requirement for delivery order. The defaulted VSZTP from VV22 will be needed to change to let say 3 if certain requirement is met.

Any user exit or badi which I could overwrite the NAST-VSZTP?

Or it is possible for me to update NAST-VSZTP using requirement inside NACE?

Kindly give me sample of source code if possible.