Plugin Tag: categories and tags converter:

Categories to Tags Converter

(16 total ratings)

Convert existing categories to tags or tags to categories, selectively.

briancolinger 50 000+ active installations Tested with 6.7.5
Taxonomy Converter

(11 total ratings)

Copy or convert terms between taxonomies.

kristarella 600+ active installations Tested with 5.2.24
Term Taxonomy Converter

(6 total ratings)

Copy or convert terms from one taxonomy to another while keeping their post associations.

Dhanendran Rajagopal 500+ active installations Tested with 7.0.1