I am having the same issue. I would like to add items to my Wix product database, however, it says it is read-only. The current fields that the default store database gives is not sufficient for what I need.
Alternatively, I tried to replicate a store by creating a new database and linking this to a repeater, however, I am unable to replicate the filter options the Wix store provides, specifically the checkboxes and slider to filter on selection.
My next step is to try and create a 301 re-direct from the store to a new dynamic page I created for each product where I can add all the extra items I need into the database. However, from other forums, it seems that this won’t work either.
Any suggestions would be great as I have been trying to figure this out for weeks!!