We asked before how to add custom fields in adding new product page.
We have followed your hints by adding the fields in new-product-single.php but to let them work properly we have had to modify also 2 core files.

When we tryed to upgrade Dokan we have inserted again the modifications in the upgraded files, but the plugin stopped working.
So we have restore the previous plugin version.

Now, how can we make the new fields working properly on the upgraded new-product-single.php and avoid future upgrade problems (or minimizing them)?

Thank you in advance.