[AccessD] Multi-value field format

A reader is considering the multi-value field for the following reason: 

"I have to format the data in this way as a last step to export to the e-commerce platform.  As I import a CSV table into the platform, it requires stuff like product name, sku, price, weight, etc.  It also has a field for category.  A product can belong to multiple categories, and the way the it imports/exports is to fill that field with the category name, separated by semicolons, in the one field.  A product can be a member of up to 20 categories (all separated by semicolons)."

I'd like to steer him away from the multi-value field. I know combining field values into a single line is a common request but I've never had to do it myself -- any suggestions? 

Thanks!
Susan H.