PO screen is deriving again the charge account when clicking it in the distribution screen

Hello ,

We are in a middle of a project where we customized the PO account generator workflow to get some specific charge accounts, those customizations are working fine, also we added some form personalizations but no matter that, when you edit the PO and in the distribution screen click the charge account field, it's derived again using the standard way (in this case is getting item expense account), the form is internally launching a routine to derive again the charge account using the vanilla routine, any idea is there is a way to identify and customize that routine?

Regards