Wix email marketing is heavily dependent on labels in order to swiftly send campaings to a specific user group, having lots of users.
However, after I had a look in the Wix API, I realized that it is not possible to change the labels of users that are already registered with an email and password on the site by means of Wix code. The Wix API states this explicitly: " You cannot use the createContact() function to update contact information for existing site members. You can use use it to update other site contacts."
I find this to be a major shortcoming in functionality. For example, if 150 people from the list of interested people “Geïnteresseerden”, which also subscribed to the site, wanted to become paying members “VOCAP leden 2018”, I essentially would have to manually change all their labels by comparing the information in the Wix CRM to my databases. As you realize, this would/will be very time consuming whilest some very simple code could do the trick. Also, as far as I am aware, Wix code does not feature in the Flinstones 
I therefore ask to expand the possibilities of changing labels as to also include existing site members. It will make my targeted email campaigns a lot swifter and save me hours, if not days of work.
Could you please verify that my reasoning is correct? Also, would you be willing to inform me if there is any foreseen update that is tackling this issue? And if not so, can it be added to the to-do list? I am quite convinced that you will be able to figure something out.
Best regards,
Chiel Buseyne
On behalf of the Flemish Society for Industrial and Organizational Psychologists