You can import multiple categories using our free Bulk Import add-on for Directory platform. You can download the add-on from Free Downloads section under your Downloads. 

Install this plugin and you will see a new section named Bulk Import/Export under the Tevolution menu in your WordPress Dashboard. The basic function of this plugin is to import multiple listings but with a trick we can also import multiple categories with it

First of all you will need a sample CSV file which you can download from the Bulk Emport/Export section under Tevolution menu in your dashboard. The sample file contains only one sample listing, what you need to do is open this sample CSV file and in the column named templatic_post_category add all your 500 categories in the comma separated format for that one sample listing.

Now, go back to the Bulk Import/Export section in your back-end and import this CSV file from the CSV Import section for listings. All the categories that you have added in the comma separated format will get imported. You can then go ahead and delete the sample listing which also got imported.