If you want to add more than one category to a listing, is it because you want to assign guides to it?
If that's the case, our advice is to create a new category that includes both qualifications you want to include.
For example:
You want to make a listing with a category Level 2 instructor and also the WFR required.
Go to Company
Click Categories
Click Create Category
Give your Category Title a name that combines the two qualifications
Click Save