Could you provide clarification on what you would like to achieve?
There are three areas potentially to cover:
TagCategory
Tag
TagAssignment
If you are thinking of backup and restore it will be necessary to cover these three areas.
The post below looks like promising for this goal, i didn't test it though.
Backup/restore vCenter tags and tag assignments | The Shell Nut
If you are thinking of automatise the creation of TagCategory, Tag and TagAssignment from a CSV it will be better to look in this direction.
http://www.virtu-al.net/2014/11/13/automating-tags-tag-category-creation-assignment-powercli/